In the Balanidæ, or sessile Cirripedes, the young animal, immediately

after the metamorphosis, or still better if dissected out of the

pupal carapace, as I succeeded in doing with _Balanus balanoides_,

may be said to be pedunculated; for it is attached by a little disc

of cement closely surrounding the antennæ, the rest of the membranous

basis forming an almost semi-globular, flexible peduncle. The valves,

at this the earliest period, are all membranous, and do not overlap

each other. In the Balaninæ they do not present the peculiar structure

of the primordial valves of the Lepadidæ; but in the Chthamalinæ, in

Chthamalus, I saw traces of this structure. Calcareous valves are

soon formed under the membranous valves. The opercular valves, at

this early period, are much larger than the valves or compartments

of the shell, which are only four in number, for the carino-lateral

compartments are not yet formed. The compartments from the first are

surprisingly strong, and have their alæ already formed and overlapped

by the adjoining compartments; but of the radii there is as yet no

trace. The four compartments form a narrow but nearly circular hoop,

which, from its relatively large diameter, tends to draw down the

upper or posterior end of the animal, now forming the opercular valves;

and as the basis soon becomes throughout cemented to the surface of

attachment, the young Cirripede is much depressed. Soon the opercular

valves are drawn a little way down within the shell, becoming attached

to the sheath, instead of, as at first, to the very summits of the

compartments. In regard to the changes which take place in the shell,

in the number of the segments in the cirri, and in the number of spines

borne on these segments, &c., during the continued growth of the

animal, as they are chiefly important for the identification of the

species, I will here refer to a discussion on this subject under the

head of the Genus Balanus.

_On the Homologies of the Carapace and Shelly Valves._

In the pupa, the carapace is produced, not only posteriorly, but

anteriorly, so as to cover the entire animal, with the exception of a

narrow sternal surface (Pl. 30, fig. 4): in front it is notched, where

the sternal surface terminates, and from this notch a faint line runs

along the dorsal surface, separating its tergal elements. In the young

Cirripede, after the metamorphosis, there is no trace of this medial

dorsal suture, or of the wider sternal surface. Looking at the several

genera of the Lepadidæ, the external covering of the whole peduncle and

capitulum is so continuous and of so uniform a nature, that I think we

must consider the whole as a carapace, of which the sternal borders

have become completely confluent; formerly I was inclined to look at

the capitulum alone as formed by the carapace, and at the peduncle as

being composed of the two or three anterior cephalic segments, cased

only by their own integuments. As far as can be discerned, the carapace

in the pupa, and consequently in the Cirripede, consists only of the

tergal elements of the segments; and this seems likewise to be the

case with the carapace of the Podophthalmia. Until lately,[67] Prof.

Milne Edwards doubted whether the carapace in the higher Crustaceans

(to which I believe the carapace of Cirripedes must be compared) was

formed by the backward production of the third segment, which bears

the second pair of antennæ, or of the fourth, _i. e._ the mandibular

segment; but from the distribution of the nerves, he now argues that

it must mainly belong to the third segment. In Cirripedes, the course

of the nerves leads to the same conclusion; for the whole shell, sack,

and peduncle are supplied with nerves proceeding from the compounded

ganglion, which belongs to the second and third cephalic segments.[68]

[67] Compare 'Histoire Naturelle des Crustacés,' tom. i, p. 27,

with 'Annales des Sciences Nat.,' 3d series, tom. xvi, 1851, p. 233.

[68] This conclusion is supported by the structure of Proteolepas:

in this Cirripede there is not a vestige of a carapace, and as

the whole of the animal in front of the mouth is almost utterly

aborted, being reduced to a mere covering to the two cement-ducts,

and as, on the other hand, the mouth with the mandibles, though

peculiarly modified, is not at all aborted, there is a strong

probability, that the abortion of the carapace is connected with

the aborted state of the three anterior cephalic segments; and that

the carapace in its origin is not any way related to the fourth or

mandibular segment.

The whole of the head in front of the mouth, together with the

carapace, is, as we know, formed of three segments; and each of these

segments, homologically, ought to consist of eight elements; I recall

to mind these facts, inasmuch as the transverse separation between the

peduncle and capitulum in the Lepadidæ, and between the basis, the

shell, and the opercular valves in the Balanidæ, might be thought to be

connected with the separation of the three cephalic segments. So again,

as in the Balanidæ the shell normally consists of eight compartments,

these might be thought to be related to the eight elements of one or

other of the three segments. But I see no reason for admitting this

view; and in the case of the carina and rostrum, two of the most

persistent and important of the compartments, they exactly cover the

sutures which ought to separate the two tergal and two sternal elements

of the segment. The valves, moreover, often form many more whorls

than three, or the number of the true cephalic segments in front of

the mouth; and in each whorl the valves tend to stand in tile-like or

alternate order, with respect to those in the whorls both above and

below, which would not be the case, if they were the eight elements of

the segments.

For the true homologies of the sclerodermic plates, or Shelly valves,

with which the external covering of Cirripedes is so generally

strengthened, we must, I believe, look to the carapace of the

Podophthalmia. In these latter, we find the carapace composed of

sclerodermic plates, which, though closely joined and only occasionally

separated by sutures, yet in their origin are distinct;[69] they

tend, also, to be arranged in alternate or tile-like order. As the

animal grows, the old sclerodermic plates, all joined together, are

moulted, and new ones, also all joined together, of a larger size,

are formed beneath. Now let us imagine the growth to be more gradual

but yet periodical, and the new and larger sclerodermic plates, when

formed under the old ones, to adhere firmly to them; the older plates

would thus be prevented from becoming confluent, and instead of

being all moulted together, as is now the case, they would be almost

continually separated from each other, owing to the almost continuous

increase in size of the new underlying plates. Consequently lines of

splitting would run between the several plates, however numerous they

might be, instead of there being, as now, a single line of splitting

extending down the back. In fact, we should have the identical manner

of growth of the shell or carapace, which occurs in Cirripedes. It is

on this ground, and from the several points of homological resemblance

incidentally mentioned in the last few paragraphs, that, in the early

part of this Introduction (p. 13), when discussing the whole class, I

stated that I believed that the carapace of Cirripedes presented more

real resemblance with the carapaces of the Podophthalmia, or higher

Crustacea, than with those of the lower Crustacea, though in mere shape

they more nearly resembled the latter.

[69] 'Annales des Sciences Naturelles,' 3d series, tom. xvi, pp.

233, 236, 237.

_Cementing Apparatus._ (Plate 28.)

I have already (p. 128) given an account of the manner in which, in the

pupa of Lepas, the cement-tissue escapes from the prehensile antennæ,

and of the structure of the cement-ducts, and of the cement-glands

or incipient ovaria; and likewise of the changes by which these

organs assume their ultimate form in the mature Cirripede. In my

former volume, on the Lepadidæ, I described the cement-glands and the

cement-tissue in several genera, and I have there shown (singular as

the fact is) that the two cement-glands, with their contents, actually

consist of ovarian tubes with their contents (for there seemed to be

a relation in the state of fulness in both) in a modified condition.

In the Balanidæ, I am not able, from the difficulty of the dissection,

to confirm these conclusions, excepting in so far that the tubes on

which the cement-glands are formed, run into the mass of ovarian cæca;

but, I may add, that in the abnormal Proteolepas, belonging to another

Order (see the section, Pl. 24, fig. 1), nothing could be plainer than

that the membrane of the ovarian sack (_b_) formed the cement-ducts,

and that their cellular contents, which within the sack (_a_) were in

process of conversion into ova, within the ducts were converted into

the cement-tissue. This cement, by some unknown power, travels down the

ducts, and debouches at the antennæ.

In the Lepadidæ, there are only two cement-glands, which are situated

high up in the midst of the ovarian cæca, with one cement-duct

proceeding from each: both the glands and ducts increase in size with

the age of the animal:[70] the cement issues either permanently from

the prehensile antenna, or, after a short period, through apertures

in the peduncle, arranged irregularly or in straight lines,--the last

formed apertures being furthest from the central and basal point of

the peduncle. In the Balaninæ, on the other hand, at each period of

growth, a pair of new cement-glands is developed, larger than those

last formed, and making, with the older glands, a chain, connected

together by what I have called the cement-trunk. The cement-trunk

consists of a tube, which generally becomes enlarged just before

entering each gland. The glands, the cement-trunk, and cement-ducts,

all adhere to the basal membrane or basal shelly plate. Each gland

gives rise to two cement-ducts, these often bifurcate, and sometimes

repeatedly bifurcate and inosculate before pouring out their contents

round the circumference of the basis; and sometimes they all first

enter a circumferential cement-duct. The probable cause of the greater

complexity of the cementing apparatus and of the greater number of the

excretory orifices in the Balanidæ, compared with the Lepadidæ, is

that the entire surface of the broad basis, which answers to the whole

peduncle in the Lepadidæ, is firmly cemented down to the supporting

object, instead of merely the basal end of the peduncle. The cement

issues either in a cellular condition, or more commonly as a fine

network, which, at a short distance from the orifices (Pl. 28, fig.

4 _a_, _z_), becomes so fine as to form a sheet or layer: I may here

recall the fact, that in the cement proceeding from the disc of the

antennæ, in some species of Lepas, a similar structure was observed.

The cement itself presents the same transparent, brown, laminated,

structureless appearance, and the same chemical reaction, as described

in my former volume. The cement has the capacity of occupying and

filling up all inequalities in the supporting surface; I have seen it,

when spread over an encrusting Flustra, present an exact model of every

cell; in the case of Coronula, it seems, as we shall immediately see,

to have the power of penetrating into, and even almost blending with

the epidermis of the supporting Cetacean. The last-formed cement-glands

and cement-ducts present a delicate and transparent appearance, and

contain cellular matter; whereas the old cement-glands, and sometimes

the old cement-ducts, are filled with brownish cement, not acted

on by boiling potash. The foregoing remarks are confined to the

sub-family Balaninæ, for I have not been able to examine thoroughly the

Chthamalinæ, and can only affirm, that in Chthamalus and Pachylasma the

cement-ducts repeatedly bifurcate and inosculate, in the same manner as

in the Balaninæ. I will now proceed to describe, in some detail, the

cementing apparatus in the several following genera.

[70] I had some slight reason to suspect in Pollicipes that new

cement-glands were successively formed: this is more probable in

this genus than in the others, inasmuch as it is the most nearly

related to the Balanidæ.

_Coronula._--The cementing apparatus is here more simple than in any

other genus of the Balaninæ, and I have studied it more carefully.

The basal membrane of _Coronula balænaris_ is figured in Pl. 28, fig.

1 _a_, and must first be described; its relation to the shell will

hardly be understood without looking at the outline of the folded walls

of this species, in Pl. 16, fig. 5. The basal membrane closes the

central circular hollow, and is continuous with rays (not represented

in Pl. 28) extending under the doubled walls and terminal transverse

loops. It has eighteen concave sides, corresponding with the inner

ends of the folded walls, for each of the six compartments is trebly

folded. The membrane consists of successive, conformable slips (_c′_,

_c′_), bordered exteriorly by thickened yellowish rims, and internally

overlapping (when viewed from the inner side) the few last-formed

slips, and then thinning out. The membrane forming each slip is itself

laminated. The middle portion, about 1/50th of an inch in diameter,

is rather opaque, owing to the slips being so close together. Beyond

this central part, the slips suddenly increase in size, but yet have

a different shape from the 18-sided outline, which they ultimately

assume: this difference is owing to the great changes in shape, as

explained under the genus Coronula, which the shell undergoes, when the

walls at first assume their folded structure. The walls are invested

by longitudinally striated membrane (_p_, _p_, _p_, fig. 1 _a_), which

turns in under their basal edges; and this membrane is united with the

basal membrane, by what I shall call the circumferential slip (_b_),

and which is shaded in fig. 1 _a_, simply for the sake of catching

the eye. It is the circumferential slip of membrane which sends

rays under the spoke-like folded walls: thin as it is, this slip is

yet laminated, but is not bordered by thickened edges. The membrane

investing the walls is, like the basal membrane, formed of successive

slips with thickened edges, which overlapping (viewed from the inside)

the last-formed slips, project beyond them, and so face the edges of

the slips in the basal membrane; they are only obscurely indicated in

fig. 1 _a_. The circumferential slip (_b_) lies over (as viewed from

within) both the basal and wall membrane. This whole structure will,

perhaps, be best understood by the sectional diagram (fig. 1 _b_),

in which the letters (_c′_, _c′_) show the slips of basal membrane;

(_p_) the parietal membrane, coating the outside surface of the walls

of the shell, not here represented; (_b_) the circumferential slip

overlying both; and (_z_, _z_) the layers of cement, which may for

the present be disregarded. In order to allow, of the growth of the

shell, the circumferential slip (_b_) periodically splits in the

middle, all round, in a line exactly conformable to the edge of the

last-formed slip of basal membrane; and likewise in straight, medial

lines under the spoke-like (cut off in fig. 1 _a_) doubled walls. I

have seen, under a high power, the line of splitting, very shortly

after its formation, with the two edges ragged and near together, with

an extremely narrow, new circumferential slip just formed, between

and over the edges of the previously formed slip. What causes the

circumferential slip to split so symmetrically, I cannot say: the

opposed edges, after a time, become thickened, apparently from adhering

to the underlying layer of cement, as will presently be described. The

circumferential slip continues increasing in breadth till the period

of its splitting arrives, by which time it has become much broader

than the last-formed slip of basal membrane; and after the splitting

takes place, the interior half towards the basal membrane, forms a

new basal slip all round the basis, and the exterior half adds a new

slip to the membrane investing the walls. This latter membrane being

inflected under the basal edges of the walls, is, during the growth of

their edges, drawn straight down, the newly-formed portion taking the

inflected position.

In the sectional diagram, (1 _b_) the circumferential slip is not yet

broad enough to split; when it has become so, it will split under

the letter (_b_). The slips of basal membrane are, as may be seen in

fig. 1 _a_, narrower towards the circumference; but the two or three

last-formed slips, are out of proportion narrower than the others; and

it is certain, from the comparison of the basal membranes of specimens

of different ages, that these will afterwards increase in width.[71]

I have seen no other instance, in Cirripedes, of growth in membranes,

except at their extreme margins: I suspect that these last-formed slips

are pulled, during the downward and outward growth of the shell, a

little from over the last-formed slips, new and larger laminæ being

all the time thrown down, so as to prevent any fissure being formed. I

also suspect that the gradual increase in width of the circumferential

slip itself, is due to the opposed edges of the underlying and

last-formed circumferential slip being dragged further apart from each

other, new and wider laminæ of membrane being continually thrown down;

the new circumferential slip being thus, also, all the time thickened,

as well as rendered broader.

[71] In the case of one _young_ shell, I found that the

previously-formed circumferential slip must have split, long before

it had assumed its proper and ordinary width; for the last-formed

slip of basal membrane was of extreme narrowness, and would have

to be considerably added to in width, whilst the new and narrow

circumferential slip was likewise being added to in width. This

slip of basal membrane, though so extremely narrow, had its own

cement-ducts and glands.

The central slip or rather disc of membrane, is 3/400ths of an inch in

diameter; and this shows the basal diameter of the shell immediately

after the metamorphosis. In the middle of this little disc I saw,

in several specimens, the prehensile, pupal antennæ; I made out

distinctly the ultimate segment with its bristles, and, as I believe,

the disc-segment, which was 7/2000ths of an inch in diameter; but this

portion was much obscured by the quantity of cement. When the corium

is removed from the inner side of the basal membrane, the two chains

of glands, extending from exactly over the antennæ in the centre about

half way towards the circumference, are conspicuous. The cement-trunk,

connecting the glands, is thin, and at the further end is always broken

off, by the removal of the corium and overlying layer of ovarian cæca,

into which the two cement-trunks enter; and without which removal,

nothing could be seen. The two chains of glands form a very large

angle, open towards the rostral end of the shell, as represented at

fig. 1 _c_, much enlarged; by a mistake in fig. 1 _a_, the two have

been drawn in a straight line. The cement-trunk increases in diameter

in proceeding from the centre to the circumference, and the glands

likewise increase in size, at the same time altering somewhat in shape.

From near the lower side (the basal membrane being viewed from within)

of each gland, two cement-ducts proceed, which pour out their contents

beneath the basal membrane. The orifices of the ducts always exactly

face the middle folds of the two lateral, and two carino-lateral

compartments. In a full-sized specimen, there are from thirty-five to

forty cement-glands on each side, always corresponding exactly with

the number of slips of basal membrane, including the circumferential

slip, to which the last-formed pair of glands and cement-ducts belong.

In correspondence with the great number and narrowness of the central

slips of membrane, so are the cement-glands towards the centre numerous

and very small. All the glands, in the more central parts, consist of

a mere transverse enlargement of the cement-trunk; but the exterior

and larger glands, which are more closely packed together, are more

globular or pear-shaped; and the two ducts (of which the one on the

rostral side is considerably enlarged at its base) do not come out of

the gland exactly at the same level. The trunk, connecting the glands,

runs straight from one to the other. The ducts proceeding from the

outer and older glands, on the carinal side, are much curved (Pl. 28,

fig. 1 _c_). To give an idea of the dimensions of the several parts, I

may state that the largest ducts were 3/1000ths of an inch in diameter,

and the glands belonging to them nearly thrice as much, measured in the

direction of the cement-trunk; on the other hand, some of the ducts

from the small central glands had a diameter eighteen times less than

that of the largest ducts. Towards the circumference, the ducts that

proceed from the older and larger glands are piled one exactly over the

other--the last formed being the topmost, and all are imbedded in the

corium which overlies the basal membrane: this position of the ducts,

one over the other (which could not be well represented in figs. 1 _a_

and 1 _c_), is owing to their all debouching at the same exact point.

But the ducts form the smaller and younger glands, when the shell

had a different shape, are spread out, and are all attached to the

basal membrane. Altogether, the basal membrane of Coronula, when well

cleaned, and examined under a moderately high power, presents the most

singular and elegant appearance.

We now come to the cement-tissue: this lies on the under or outer

side of the basal membrane; it is not represented in figs. 1 _a_ or

1 _c_, but only in the sectional diagram, 1 _b_, by the letters _z_,

_z_: it presents its usual character and appearance, like solid glue

or brown gum, but is obliquely laminated and sub-laminated: it forms

a layer, much thicker than the basal membrane itself, being as much

as .004 or .005 of an inch in thickness. It is, however, difficult

to ascertain its thickness, from the singular manner in which it

penetrates into and almost blends with the epidermis of the whale's

skin; so much so, that for a considerable time I thought (not then

knowing anything about the cement of Cirripedes) that this transparent

horny substance probably answered to a corn on the human foot produced

by pressure. But I soon observed that this horny substance certainly

extended into and up the cement-ducts; and this fact first led me to

the examination of the whole subject in the several genera of Lepadidæ

and Balanidæ. It was not difficult to remove the cement-ducts, leaving

small portions of the contained cement projecting freely up as points

from the general surface of cement. The cement adheres slightly to the

whole basal membrane, but chiefly to the yellowish rims or edges of

the successive slips; and it is indeed this adhesion which, I believe,

produces the rims; for the circumferential slip, when first split, had

very thin ragged edges. The cement also extends under the spoke-like

prolongations of the circumferential slip, and likewise some way up the

sides of the walls.

The cement-glands, the trunk, and the ducts, except the two, three,

or even four last-formed ones, are all filled with an apparently

solid thread of transparent, brownish cement, differing in no respect

from the cement under the central parts of the basal membrane. In

one instance, in which the last-formed pair of glands and ducts had

apparently been only just developed, they were so perfectly transparent

that I could distinguish them only under certain lights, and I could

not perceive any contents. The last-formed glands and ducts always

appear very delicate, and include a tube of very delicate tissue,

containing more or less of granular matter. The next succeeding pair of

glands and ducts are always more opaque, and contain much more granular

matter; which, in the next, or next but one, may be seen passing into

the state of pale brown, transparent chitine. I have seen some most

distinct instances, in which, in the same duct, the part towards the

centre of the basis was filled with homogeneous cement, and the part

towards the circumference with still plainly granular matter. In the

successive circular slips of cement-tissue, lying attached under the

circumferential slip and under the two or three succeeding slips of

basal membrane, an exactly analogous series of changes is presented; as

indeed might have been expected, as the slips of cement are absolutely

continuous with the contents of the ducts. Moreover, if a vertical

section be made across one of the last-formed slips of cement, it

may sometimes be seen to be apparently in the act of separating into

layers, with the lower layers more pulpy, elastic, and white than the

upper layers, which are less coherent, and show as yet even still less

the character of cement. The cement under the circumferential and

adjoining slips, often presents a peculiar wrinkled appearance, in

lines conformable with the outline of the basal membrane; but I do not

believe that these are real wrinkles, though so like them; they seem

to consist of sinuous threads, longer or shorter, sometimes slightly

branched, crossing and inter-joined, and composed apparently of faintly

coloured cement. I suspect that these threads are formed by the union

and subsequent drawing out of aggregations of that matter, which within

the ducts is first granular, and then changes into cement; for at the

orifices of the ducts these wrinkled threads sweep outwards in curved

lines on both sides. The cement in these early stages adheres, with

very little force, to the basal membrane; and with only a little more

force to the underlying layers of cement; in fact, till it assumes the

brown translucent appearance, like solid glue, it hardly seems to act

as cement.

How the cement reaches the skin of the whale, will be best understood

by referring to the sectional diagram (Pl. 28, fig. 1 _b_). When the

circumferential slip of membrane (_b_) splits, a new circumferential

slip will be formed over it, together with new cement-glands and

ducts, and cement (_z_, _z_) will issue from four new orifices, and

will extend on both sides of these orifices, till the ends meet and

become united, thus forming a narrow, 18-sided, continuous, new slip

of cement, with 18 spokes proceeding from it. I have not noticed lines

of union in the cement of any one slip; but the matter forming each

slip, certainly has proceeded from four distinct orifices. Seeing how

perfectly successive layers of cement often become blended together,

lines of union or junction, could hardly be expected to be preserved

in the same individual layer. When the circumferential slip of basal

membrane splits, the underlying slip of cement, which we will call A,

does not split, but becomes stretched, so that the newly formed slip of

cement, which we will call B, does not reach the skin of the whale. As

the new circumferential slip of basal membranes goes on increasing in

width, A continues to be stretched, but does not split, till at least

another circumferential slip of basal membrane has been formed and

has been split, and till B has been also stretched. By this time, the

cement-tissue A has assumed its normal structure, and has the power of

adhering to the whale's skin, which it has now reached, owing to the

splitting of the under and older slips of cement. At the next period

of growth, A itself will split, and B will touch the whale's skin and

adhere to it; and this, also, will ultimately split. It results from

this action, that the cement has a stretched, and sometimes even a

fibrous appearance, with the lower edges of the layers, of which each

slip of cement is formed, thinning out. I have before stated, that the

two or three last-formed slips of basal membrane are formed at first

too narrow, and apparently have to be dragged outwards, over each

other; and it is perhaps owing to this circumstance, and to globules of

cement having first adhered to the under surface of the slips of basal

membrane, that these slips are studded beneath with parallel little

vermiform bodies, sometimes of considerable length, and furnished

with heads, all directed outwards. These tapering, vermiform bodies

have a considerable resemblance to the threads before mentioned,

which give the wrinkled, concentric appearance to the newly-formed

layers of cement, and have probably a closely analogous origin: in

one case, indeed, it appeared as if some of these concentric threads

were in process of being drawn out at right angles to their original

course. Lastly, it should be observed, that as the exterior half of the

membrane of the circumferential slip, after each splitting, is dragged

down, and thus comes to invest the outer surface of the wall of the

shell (the wall not being represented in the diagram, but standing

where the letter (_p_) stands), so it must be with the cement, which

thus likewise comes, in an unusual manner, to invest the outer surface

of the folded walls of the shell, and attaches them to the skin of the

whale,--which latter is always growing upwards, and tending to bury the

shell.

_Platylepas decorata._--This genus is closely allied to Coronula,

and the cementing apparatus is essentially similar. In one specimen,

I counted no less than forty-nine slips of basal membrane, each of

which, of course, had its pair of cement-glands, and each of the

latter its two ducts. The glands consists of a transverse enlargement

of the trunk, as in the early stages of Coronula. Neither the glands

nor the duct, when old, become filled up with cement, but only the

main-trunk. The ducts are very delicate and thin; the larger ones being

only 3/10,000 of an inch in diameter. The glands stand some way apart

on the two cement trunks; and the latter, instead of being straight

as in Coronula, are deeply serpentine; the glands are formed on each

bend, so that, though all on one side are connected on the same trunk,

they form a double row on each side of the basal membrane. The basal

membrane (in the centre of which I distinctly saw the antennæ of the

pupa) has six deep bays or excisions, corresponding with the midribs

(see Pl. 17, 1 _a_, 1 _d_) of the six compartments; and the two ducts

from each gland, on the right and left sides, debouch at the heads of

the four lateral excisions, exactly opposite the midribs of the lateral

and carino-lateral compartments. The later-formed glands, owing to

all of them being situated some way apart from each other on the two

cement-trunks, lie further from the centre of the basis than do the

orifices of their ducts; hence the later-formed ducts are directed a

little backwards, or from near the circumference towards the heads of

the deep excisions.

_Tubicinella._--The cementing apparatus is here less symmetrical; but

this, I believe, is chiefly owing to the basal membrane being formed

of successively larger discs (not slips) of membrane, thrown down not

quite concentrically one over the other; each new disc of membrane

seems to cover the last-formed cement-glands and ducts; and there

are as many ducts and glands as there are discs of membrane, all

adhering together. In one specimen, it appeared that normally there

were four sets of cement-ducts, as in the allied genera of Coronula and

Platylepas; but in other specimens, the ducts were distributed very

irregularly. In one case the two cement-trunks extended parallel and

close together, one of them terminating long before the other. I have

given a figure (Pl. 28, fig. 3) of three of the cement-glands, removed

from the basal membrane, together with their ducts. The cement-trunk

(_f f_) seemed to be a little enlarged, and to be crossed by septa, as

it entered the glands (_h_), but I could not make out this structure

clearly enough to be represented. Whilst young, the cement-glands stand

some little way apart from each other; and in the figure given of some

of the last-formed glands, they are hardly separate enough. Each gland

gives out obliquely, on one side, a cement-duct (_c_) which I traced

in several cases to the margin of one of the discs of basal membrane,

where cement issued from it; and on the opposite side, a tapering spur

(_b_), varying in length, which may be called, and I believe really

is, a rudimentary duct. Of these spurs we shall meet many instances

in other genera. The duct (_c_) and the spur (_b_), close to where

they entered the gland, in some specimens gave off, at about right

angles, short blunt points, or rudimentary branches. This duct and spur

correspond, I believe, with the two ducts in Coronula; but besides

these, a duct (_a_) is given off from one end of the gland, from the

surface opposite to that at which the cement-trunk enters. This duct

(_a_) is very singular, from always forming a loop (_a′_), with two

spurs projecting from it: these two spurs occasionally spring from a

common point: I have seen nothing like this structure in any other

Cirripede. This duct (_a_) runs, like the duct (_c_), to the margin

of its own disc of basal membrane, where it debouches. Besides these

ducts, in the best specimen which I examined, there were two other

sets of ducts, which were slightly zig-zag, and at each angular bend,

a mere knob or point, or at most a short branch, was given off; but

this branch seemed never to run to the margin of the basal membrane

or to give out cement; whereas the main branch did give out cement. I

was not able to trace these ducts to their glands. In these zig-zag

ducts, and in the rudimentary points sometimes observed at the base

of the duct (_c_), and likewise at the base of the spur (_b_), we see

the first indication of that tendency to bifurcation, so strongly

characteristic of the cement-ducts in all the genera, excepting those

already described, which are allied to Coronula.

_Chelonobia patula._--The cementing apparatus is here chiefly

remarkable for the thinness and straightness of the main trunk, (_f f_,

Pl. 28, fig. 2), and from the great distance at which the glands stand

apart; had another gland been drawn, it would, on the scale here used,

have stood exactly under the two upper, (_c′ c′_) in fig. 1 _c_. We

here see that the trunk (_f_), before entering the gland (_h_), has an

enlarged portion (_g_); this, I suspect, is a very general structure.

Each gland gives out, on opposite sides, two ducts (_a a_, _b b_),

larger even than the main trunk; and these ducts bifurcate repeatedly,

and inosculate. By this inosculation it is not improbable that all four

ducts, proceeding from the two glands of the same age, may be connected

together; certainly the bifurcating branches from the same duct thus

become repeatedly connected. For the first two or three bifurcations

the ducts decrease very little or not at all in diameter; but nearer

the circumference they become smaller. The ducts, also, proceeding

from the younger and smaller glands, are, of course, proportionably

smaller. In one case I was able to count four bifurcations in the duct

between the gland and the edge of the basal membrane. It follows from

this structure, that the basal membrane, at each period of growth,

is cemented down by cement issuing from several orifices; but we

shall presently find that in other genera the cement proceeds from

many more orifices. In fig. 2 there is represented, by the aid of the

camera, a small portion (from the outer (_a_) to the outer (_b_) being

12/100ths of an inch in length) of the basal membrane, with all the

several cement-ducts adhering to it, which I could distinguish, and

drawn of their proper relative sizes; this figure also shows some of

the bifurcations, but no inosculation happened to be included in the

space here given; the basal membrane itself has not been represented.

In taking a view of a considerable portion of the basal membrane,

especially towards the circumference, some parallelism in the branches

could be perceived; one set of branches tending to run in the direction

of the ray of the circle, and the other set in the line of the

circumference.

_Elminius Kingii._--The cement-glands here resemble those of

Chelonobia, but the trunk does not seem to be enlarged before

entering the gland. The glands are situated rather far apart; and

the chief peculiarity is, that the trunk connecting the glands is

as tortuous as the track of a worm. Each gland gives out two ducts,

which bifurcate repeatedly, and often inosculate, making, in parts,

an hexagonal mesh-work: some of the branches do not debouch on the

basal membrane, but terminate in blunt points. So numerous are the

ducts, that the basal membrane may be compared to pieces of paper

with the fine fibrous branching roots of some plant dried and heaped

on it. Some of these ducts are very regularly jointed, and resemble

a conferva,--an appearance which I believe is owing to divisions in

the contained cement; other ducts are partially marked by little

wrinkles, as presently to be described under Balanus. The cement,

instead of, as heretofore, invariably forming a slip round and beneath

the circumference of the basal membrane, here often forms little,

independent, circular, and irregularly-shaped discs, each of which has

issued from a single orifice. I may here add that in two species of

_Tetraclita_ I saw the cement-ducts repeatedly bifurcating, with some

of the branches inosculating, as in Elminius and Chelonobia.

In _Balanus balanoides_, which, like all the Cirripedes hitherto

mentioned, has a membranous basis, I could only make out an amazing

number of bifurcating and inosculating cement-ducts, of very various

diameters. The cement-tissue, on the under side of the basal membrane,

generally consisted of little circular discs, on an average from 2 to

5/1000ths of an inch in diameter; but there were also globules and

short tortuous threads of cement. In some very much elongated and

crowded specimens--in which, during the downward growth of the walls,

the basal membrane had ceased to reach the surface of attachment, and

being thus suspended had become, as viewed from the outside, deeply

concave--the cement had apparently continued to try to reach the rock,

and now hung down in the form of two thickish roots, some tenths of

an inch in length. These roots were round, and tapered either to a

fine or blunt point; one was doubled on itself, and so had become

united; in the other, I could perceive five layers or sheaths of the

cement-tissue, one within the other; the innermost of these layers,

which once, no doubt, formed the outside surface of the root, was only

a quarter of its present length.

In _Balanus tintinnabulum_, the basis is calcareous: when its upper

surface is cleaned, dried, and examined under a good light, the

numerous larger cement-ducts can be seen, even by the naked eye, or

under a weak lens, and present an elegant appearance. These larger

ducts run in parallel lines from the two chains of glands towards the

circumference. They are all encrusted with calcareous matter, and in

the more central parts are hidden under it; at each period of growth,

when the basis is added to round the circumference, it would appear

that a layer of excessive tenuity of shell is thrown down over the

whole surface, just in the same way as in Tubicinella, at each period,

a new and larger disc of membrane was thrown down over the pre-existing

membranes with their cementing apparatus. The cement-glands, in the

middle of the basal plate, seem often to give rise to small abnormal

depositions of calcareous matter. When the basis (it is best to take

a young specimen) is slowly dissolved in acid, all the cementing

apparatus is left uninjured, adhering to the delicate tissue which

before existed in a calcified condition. Near the middle I saw the two

antennæ of the pupa; and from them the two cement-trunks extended about

half-way towards the circumference. These two chains of glands are

often placed very irregularly, but they tend to form, as in Coronula,

a large angle, open towards the rostral end of the shell. The glands,

close to the old antennæ, commence abruptly, of rather large size: the

later-formed glands, with their ducts, are in regular order larger than

the younger ones, and stand much closer together. After immersion in

acid all the glands and ducts appeared empty, instead of the older

ones being, as in Coronula, filled with cement. In one case I counted

on each trunk twenty-five glands, besides some smaller obscure ones

close to the centre.

In Pl. 28, fig. 4 _b_, I have given a drawing of two of the cement

glands: the cement-trunk (_f f_) is smooth and apparently cylindrical:

it becomes enlarged (at _g_) before entering the gland: it seems even

to be prolonged across the gland under the form of a narrow bar (not

represented), which apparently serves to keep the two ends of the

trunk, on the two sides of the gland, in their proper relative places

and distances. The gland itself is an elongated bag (_h_), which

properly lies exactly over the enlarged portion (_g_) of the trunk,

but in the drawing has been purposely displaced: it gives rise, in the

later-formed glands, to a sort of neck (see the upper gland), which

is either so long as to deserve rather to be called a duct and which

soon bifurcates, or is quite short (see the lower gland) and gives rise

to two separate ducts. On the opposite side of these glands, there

is a spur (_m_), of greater or shorter length, which is evidently a

rudimentary duct, for in the younger glands it existed as a perfect

duct. Moreover, the first-mentioned duct often gives off branches

(_t′_), having an exactly similar appearance with the spur (_m_). The

membrane of which the cement-trunk (_f_), with the enlargements (_g_),

is composed, is smooth, but that of the glands and of all the ducts,

presents a very peculiar appearance, which at first would be called

scaled, but more properly perhaps notched,--each notch being apparently

formed by a line of thickened membrane, extending obliquely round only

a short portion of the tube, and indenting it. The ducts, which I

measured, were between 1/3000th and 4/3000ths of an inch in diameter.

In fig. 4 _a_, I have given a drawing of the two chains of glands, but

with only those ducts figured which proceeded from the last-formed

pair of glands. The specimen here drawn was old; and it is rare to

find the structure of the ducts so simple. From both glands[72] a neck

or thick duct arises, which soon bifurcates; one branch runs direct

into the circumferential duct, and the other (_t_) bifurcates again;

of the latter, one branch unites with its fellow from the opposite

gland, and then forming a single duct (_t′_) enters, as do the two

other branches, the circumferential duct. Thus, into the latter, five

main ducts enter: the position of their points of entrance, with

respect to the shell, varies considerably; but I think the five points

tend to face the middle of the rostrum, and middle of the two lateral

compartments on each side. In some other specimens, in which the

ducts were nearly as simple, I observed that the neck or main duct at

once divided into three branches, instead of into two, with one soon

bifurcating; and on one side a rudimentary branch or spur was given off

(above _t_), indicating a tendency to an additional bifurcation. In

the later-formed glands, the ducts proceed only from the outer sides

and form the ends of the glands furthest from the centre; but in the

earlier-formed and smaller glands of the same individual, other ducts

proceed from the inner sides, where in the older glands the spurs (_m_)

are situated: moreover, in the younger glands, all the ducts bifurcate

much oftener (how often I was not able to ascertain), before entering

the circumferential duct; many of the branches, however, terminating in

spur-like points. Now if we imagine twenty or thirty repetitions of the

ducts given in fig. 4 _a_, (independently of the greater complication

of the ducts of the younger glands), each a very little smaller than

the other, and placed, with the main branches parallel, one over and

within the other, we shall gain some insight into the wonderfully

complicated structure of the cementing apparatus in this and many other

species of Balanus.

[72] It should be observed that fig. 4 _b_ ought to have been drawn

with its present upper end downwards, to make it correspond in

position with fig. 4 _a_.

I have as yet only alluded to the _circumferential duct_ (_i_, _i_, Pl.

28, fig. 4 _a_): we have not hitherto met with this duct, but I suspect

that the branches which in Chelonobia inosculate, and which seem to

run nearly parallel to the circumference of the basal membrane, answer

the same purpose of connecting the ducts together, and are, perhaps,

strictly homologous. In this, and some other species of Balanus, the

last-formed circumferential duct runs round the margin of the upper

lamina of the basal plate, close to the basal edges of the walls; and

as these latter have projecting longitudinal ribs, the duct curves

a little round each rib; so that the whole duct is formed by as many

short inwardly curved portions as the walls have ribs, or longitudinal

septa. Between the basal extremities of these parietal, longitudinal

septa, the extremities of the radiating septa of the basis project

and enter; and along the crests of the latter, little branch-ducts

(_i′_), proceeding from the circumferential duct, extend. In the basis,

beneath the tubes formed by the just-mentioned radiating septa, there

is a cancellated shelly mass (which, in fig. 4 _a_, was of unusual

thickness), and along the crests of the branching ridges forming this

cancellated mass, the sub-branches of the above branch-ducts (_i′_)

run; these soon become so minute as not to be distinguished by the

highest powers, and thus form a sheet of cement, which attaches the

last-formed zone of the shelly basis to the supporting surface. At

what point the membrane forming any one duct ceases, the cement-tissue

being alone left, I was not able to ascertain; but the lower parts

of the reticulated slip (_z_, _z_, fig. 4 _a_) closely resembled the

cement-tissue which surrounds the disc-segment of the pupal antennæ

in _Lepas australis_. The circumferential duct, here and there, forms

little loops, as may be seen in fig. 4 _a_: and often two branches,

running along the crests of two adjoining basal septa, proceed from

a common point of the circumferential duct. The cement itself, under

different parts of the basis, appears as little separate discs, as

threads, globules, and as a fine network, but most commonly as simple

layers. As each thick zone of shelly matter is added round the basis,

the exterior branches of the ducts, between the circumferential duct

and the new layer of cement beneath, are fairly imbedded in shell, and

are for ever hidden, without, indeed, acid be used for the dissolution

of the calcareous matter: so, also, the pre-existing ducts and glands,

and the main trunk, would all have been hidden, if the layer of

calcareous matter, which, I believe, is thrown down at each period of

growth over the entire surface, had not been of excessive tenuity.

I cursorily examined the cementing apparatus in _Balanus galeatus_,

_improvisus_ and _crenatus_, which have all calcareous bases, and

belong to different sections of the genus; and the structure seemed to

be essentially the same. In _Bal. galeatus_, I found the cement-ducts

varying in diameter from 1/4000th to 1/10,000th of an inch in diameter.

In _B. improvisus_, the cement-glands do not differ much from those

of _B. tintinnabulum_; but the cement-ducts bifurcate often before

entering the circumferential duct; and the little branches, which

proceed from the latter, are very short, and almost immediately, owing

to the thinness of the basis, blend into a slip of cement.

* * * * *

I hope to be excused for describing at such length, the apparatus by

which sessile cirripedes are permanently attached to a supporting

surface; for this is the great leading character of the sub-class,

not hitherto observed in any other Crustacean.[73] It is not easy to

overstate the singularity and complexity of the appearance of the

basal membrane of a Balanus or Coronula: and when we consider the

homological nature of the apparatus, the subject becomes still more

curious: I feel an entire conviction, from what I have repeatedly

seen in several genera of the Lepadidæ, both in their mature and

pupal condition, and from what I have seen in Proteolepas, that the

cement-glands and ducts are continuous with and actually a part of an

ovarian tube, in a modified condition; and that the cellular matter

which, in one part, goes to the formation of ova or new beings, in the

other and modified part, goes to the formation of the cementing tissue.

To conclude with an hypothesis,--those naturalists who believe that

all gaps in the chain of nature would be filled up, if the structure

of every extinct and existing creature were known, will readily admit,

that Cirripedes were once separated by scarcely sensible intervals

from some other, now unknown, Crustaceans. Should these intervening

forms ever be discovered, I imagine they would prove to be Crustaceans,

of not very low rank, with their oviducts opening at or near their

second pair of antennæ, and that their ova escaped, at a period of

exuviation, invested with an adhesive substance or tissue, which served

to cement them, together, probably, with the exuviæ of the parent,

to a supporting surface. In Cirripedes, we may suppose the cementing

apparatus to have been retained; the parent herself, instead of the

exuviæ, being cemented down, whereas the ova have come to escape by a

new and anomalous course.

[73] Rathke has described ('Acta Nova,' 1839, p. 147), in some

siphonostomatous crustaceans, a pair of curious organs, which serve

to secrete a substance that holds the eggs attached together in a

mass to the parent's body: these organs Rathke has designated by

a similar name to that which I have used, namely, the cementing

organs or receptacles; they are distinct from the oviducts, but

enter them near their external orifices. As in Cirripedes, the

cement-glands and ducts are certainly continuous with an ovarian

tube; and as they occupy a quite different position in the animal's

body, these organs of Rathke, though in some degree analogous in

function, must be homologically distinct.

_Affinities, Classification, Variation._

Under the Order it has been stated that the Balanidæ, are, on the

cirripedial type, the highest in the class; that is, they are the

most complicated, but not (to use Professor Owen's term) by mere

vegetative repetition. Amongst the Balanidæ, the first section of the

genus Balanus may be taken as typical; here we have the structure of

the shell extremely complicated, yet beautifully adapted for strength,

and for the protection of the included body. The cementing apparatus

is here, also, most complicated. I have divided the Balanidæ into two

natural sub-families, the Balaninæ and Chthamalinæ, in accordance

with certain differences in the structure of the shell and of the

animal's body: that this division is natural, might almost be inferred

from the one fact, that all the characters by which the Chthamalinæ

differ from the Balaninæ, are those by which the former approaches

the family of the Lepadidæ; moreover, certain anomalous characters

in the Chthamalinæ, as the supplemental whorls of compartments in

Catophragmus, and the presence of caudal appendages in this same genus

and in Pachylasma, reveal this same affinity. The only objection which

I can see to the separation of the sixteen genera into the above

two sub-families, may be drawn from the degree to which they blend

together; thus, as far as the shell is concerned, Chelonobia, in one

important internal point of structure, tends to assume the character

of the Chthamalinæ; and on the other hand, Pachylasma, a member of the

Chthamalinæ, has a shell, which if not examined during its earliest

growth, would be placed without doubt amongst the Balaninæ. But it

fortunately so happens, that in no one character of the body does

Pachylasma approach the Balaninæ more nearly, than do the other members

of its sub-family; or Chelonobia approach, in the same respects, the

Chthamalinæ. It is only in Chthamalus, of which the shell clearly

places it in the sub-family bearing its name, that in some of the

species, the less bullate labrum,--the larger palpi,--the lower teeth

of the mandibles being laterally double,--and the lower segments of

the third pair of cirri being thickly clothed, like the lower segments

of the second pair, with bristles--all show that these species make an

approach in structure to the Balaninæ.

It will be seen that I have divided the Balaninæ into two little

groups, according as whether the branchiæ consist of one or of two

plicated folds of membrane, and as whether or not the scutum and

tergum are articulated together. I have been greatly tempted to

follow Drs. Leach and Gray, who have separated the second of these

groups, containing the genera Coronula, Tubicinella, Xenobalanus,

and Platylepas, into the sub-family of the Coronulinæ. Certainly

these genera have a peculiar aspect in common, and agree in being

parasitic and imbedded in the skin of Cetaceans, as is the case

with the first three genera, or in that of turtles, manatee, and

sea-snakes, as in Platylepas. Though these genera possess several

peculiar characters, yet I can find none common to all four, excepting

their imbedment in the skin of Vertebrata, their double branchiæ, and

their non-articulated opercular valves; and these I do not think of

sufficient importance to serve for the separation of a sub-family; for

in Chthamalus, one species has double branchiæ, one species has no

branchiæ at all, and the other species have single branchiæ; so again

in Chelonobia, the scutum having only a horny articular ridge, makes

an approach to Coronula and its allies. I may further specify that the

folded walls, a singular character common to Coronula, Platylepas and

Xenobalanus, fails in Tubicinella; the open tubes and the imperfect

outer lamina of the parietes towards their bases, are characters which

fail in one species of Platylepas; the muscles running to the opercular

valves being thinly spread out, and partially without transverse striæ,

is also a character which fails in Platylepas; the simplicity of the

cement-ducts partially fails in Tubicinella; and lastly, the existence

of small intermediate teeth on the mandibles, fails in Xenobalanus:

hence, I repeat, I have not thought it prudent to admit the sub-family

of the Coronulinæ though in many respects a very natural group.

The genera in the Balaninæ and Chthamalinæ are founded chiefly on

the number of the compartments (the number being apparently due, as

previously explained, to the fusion or abortion of certain of the

eight typical compartments); and secondarily, on the nature and even

form of the basis, and on the porosity of the walls. In Coronula and

its allies, the non-articulated opercular valves and deeply folded

walls come into play. As a justification for using these characters in

distinguishing the genera, and even to a certain extent in separating

the two sub-families, I must call to mind that the shell, with the

basis, is not merely a dermal envelope, as amongst Molluscs, but

actually consists of the first three segments of the head. The parts of

the mouth and the cirri are of very little service in distinguishing

the genera,--a singular fact, considering that most of the genera

amongst the Lepadidæ could be distinguished by these organs,--though

trifling details in their structure sometimes come in useful as

specific characters. Balanus, with the sub-genus Acasta; Pyrgoma, with

the sub-genus Creusia; Tetraclita, and Elminius, are genera of about

equal value; though perhaps the two latter are rather more nearly

related together than to the others. Chelonobia is more distinct; it

shows some little affinity to the Chthamalinæ, and likewise to the four

following genera. Coronula, Platylepas, Tubicinella, and Xenobalanus,

are genera quite distinct from the foregoing, and from each other;

yet, as we have just seen, palpably allied together. Amongst the

Chthamalinæ, Pachylasma, Octomeris, and Catophragmus, are more closely

related to each other than to the other two genera of the sub-family;

yet Pachylasma, as far as the shell is concerned, leads into the

Balaninæ, and Catophragmus into the Lepadidæ; Octomeris leads towards

Chthamalus, and Chthamalus towards Chamæsipho.

_Variation._--The discrimination of the species in most of the

genera, offers very great difficulties. I cannot too strongly impress

on any one intending to study this class, not to trust to external

characters: he must separate and clean, and carefully examine the

internal structure and form of the compartments, and more especially

of the opercular valves. After considerable experience, when numerous

varieties of a species have been carefully examined, the eye acquires a

sort of instinctive knowledge, by which it can recognise the species,

though the character cannot be defined by language; but I have found

that no amount of experience with some of the commonest species,

will save frequent and grave errors, as long as external characters

alone are trusted to. Not only does every external character vary

greatly in most of the species, but the internal parts very often

vary to a surprising degree; and to add to the difficulty, groups of

specimens not rarely vary in the same manner. After having given up

several years to the study of this class, I must express my deliberate

conviction that it is hopeless to find in any species, _which has a

wide range, and of which numerous specimens from different districts_

are presented for examination, any one part or organ,--which from

differing in the different species is fitted for offering specific

characters,--absolutely invariable in form or structure. I may in one

respect even go further, and affirm, that, if in a species, any part or

organ differs remarkably from the same part in its congeners, then if

many specimens are examined, especially when collected from different

districts, such part or organ will be found _eminently_ variable. I

may instance the antenniformed third pair of cirri in _Chthamalus

antennatus_, the teeth on the posterior cirri in _Acasta sulcata_,

the terga in _Pyrgoma dentatum_, the adductor ridge of the scuta in

_Pyrgoma cancellatum_ and in Creusia, and other such cases: hence it

will not do to found a species on a slight, or sometimes even on a

considerable difference, in _any single point or organ_. On the other

hand, I am far from asserting, that if only half-a-dozen specimens of

some rare species of Cirripede be brought from some one quarter of the

world, characters beautifully defined may not be readily discovered. In

determining what forms to call varieties, I have followed one common

rule; namely, the discovery of such closely-allied, intermediate forms,

that the application of a specific name to any one step in the series,

was obviously impossible; or, when such intermediate forms have not

actually been found, the knowledge that the differences of structure in

question were such as, in _several allied forms_, certainly arose from

variation,--for instance, in the case of two shells otherwise identical,

one being longitudinally ribbed and the other smooth, a character which

we know to vary,--but I have always used this argument from analogy with

great caution. Finally, as in the large genus Balanus, there is an

especial amount of variation, I have there entered in detail on this

subject; and I hope that those interested in it, will refer to that

discussion, which is almost verbally applicable to some other genera of

the family, as Tetraclita and Chthamalus.

_Rate of Growth, Exuviation, Powers of Repairing Injuries._

In my former volume I have shown that the pedunculated cirripedes

grow rapidly; this is likewise the case with the Balanidæ. Mr.

Stutchbury informs me that he has seen numerous specimens of _Balanus

tintinnabulum_ from 2 to 3 inches in height and from 5 to 6 inches

in circumference (and this is nearly the full size which the species

attains), on a vessel which had been to sea only during one year. At

Coquimbo, in Chile, I have seen a specimen of _B. psittacus_ 1.3 of

an inch in basal diameter, and .8 in height, adhering to a chain that

had been only six months under water. Poli, also, gives the case of

some Balani (probably _B. perforatus_), which, in about four months,

had attained a basal diameter of 1 inch, and a height of 1-1/6th of an

inch. _Balanus balanoides_ is a smaller species, and of slower growth;

for the late Mr. W. Thompson, of Belfast, found that in three months

from July 3d, certain marked specimens had increased from 2-1/2-3

lines to 4-1/2 lines, which is the usual maximum size attained in that

locality. From other observations, Mr. Thompson believes that the

extreme duration of life of this species is about two years: whether

the other and apparently quicker-growing species, are shorter-lived, I

have no means of judging.

In accordance with this rapid growth is the frequency of the periods

of exuviation. Mr. Thompson kept twenty specimens of _B. balanoides_

alive, and on the twelfth day he found the twenty-first cast-off

integument, showing that all had moulted once, and one individual

twice, within this period.[74] This frequency of exuviation, together

with the durability of the cast-off integuments, explains the

astonishing masses of exuviæ, which Mr. Peach assures me he annually

has observed off the coast of Cornwall; they are most abundant in

April and May, but he has seen quantities also in September; he could

easily, as he tells me, have filled several quart-measures with them.

The specimens sent to me consisted chiefly of _Balanus balanoides_,

_perforatus_, and _Chthamalus stellatus_. The opercular membrane,

with a narrow strip from between the two scuta, and another narrow

strip from between the two terga, are moulted together, in connection

with the more delicate membrane lining the sack, and investing the

plicated branchiæ. This membrane, likewise, is continuously connected

with that covering the whole body and its appendages. As I have stated

under the Lepadidæ, the inner tunic of the œsophagus, of the rectum,

of the olfactory pouches, and that which enters a little way into the

acoustic meatus, and the apodemes of the maxillæ, are all moulted.

On the cirri and jaws, new spines are formed with their upper ends

enclosed within the old spines, but with their lower ends projecting

inwards, beyond the bases of the old spines, and inverted like the

fingers of a glove hastily pulled off. The membranes of the body, in

the act of exuviation, split, I believe, only over the prosoma. How the

neat separation of the opercular membrane, from all round the sheath

and opercular valves, is effected, I do not fully understand; but it

is, probably, analogous to the splitting of the thick carapace of the

common crab. I suspect in Coronula, in which genus and its allies the

opercular membrane is not periodically moulted, that the membrane

lining the sack is not always thrown off at the same exact time with

that of the body. In _Chthamalus stellatus_, in the act of moulting,

the opercular membrane is the last part that separates from the new

underlying membranes: I find that this species can moult when kept in a

damp box out of water. The new membranes of the body, immediately after

the exuviation, are not lax in any extreme degree. The exuviæ of the

genus Chthamalus, and of some other genera amongst the Chthamalinæ, can

at once be recognised by the divergence of the posterior _four_ pairs

of cirri: in the case of _Chthamalus stellatus_ I have also noticed

that the animal generally dies with these cirri in the same divergent

position. Finally, I cannot doubt[75] that the Triton described by

Linnæus was only the exuviæ of some Balanus (probably _B. porcatus_);

Linnæus mistaking the probosciformed penis for the mouth of his

imagined distinct animal.

[74] In Daphnia, Straus ('Mém. du Museum,' tom. vi, p. 151) found

that the individuals moulted every five or six days.

[75] Linnæus speaks of the included body (inhabitant as he calls

it) of other Cirripedes, as a Triton; and this, I think, shows

that Lesson's conjecture that the Triton was an Alepas cannot be

correct; for Linnæus could hardly have supposed that a pedunculated

cirripede inhabited another pedunculated or sessile cirripede.

I have seen a few specimens showing that when the shell has been broken

it can be repaired; and this I believe is effected by the growth

of a crest of corium between the broken edges, and the subsequent

calcification of this crest. Mr. Stutchbury possesses a monstrous

specimen of _Chelonobia testudinaria_, in which one of the lateral

compartments on one side has not been developed. The cirri not rarely

get cut off, but are, as it appears, soon repaired. I have observed

a singular number of examples of the act of reparation in a group of

the Australian _Balanus vestitus_. The manner in which the cirri are

repaired seems to me curious: the cut-off end is closed by a rounded

scale of yellowish chitine, and then the corium, in the four or five

subjacent segments, separates from the external articulated membrane,

which now serves only as a case or capsule. The tube of corium thus

enclosed, with its contained muscles, shrinks a little, and soon can be

perceived to be in process of dividing into new and smaller segments,

in one instance ten in number,--which at the next exuviation would, no

doubt, be invested with an external membrane, and be freely exposed. In

another instance, the pedicel of a posterior cirrus had been cut off

and subsequently closed; in this instance, a whole, immature, miniature

cirrus, with the two rami, each having fifteen minute segments, was

thus enclosed in what had been the single lower segment of the pedicel.

I have seen several specimens of _Balanus balanoides_, as described

under that species, with several of the cirri and the penis truncated;

but I believe this was owing to monstrosity, which seemed particularly

to affect the male organs of generation; for no reparation seemed to be

in progress. In a specimen of Coronula, however, the penis appeared to

have been really cut off by accident; it had been closed, by a scab,

with concentric lines, like the articular rings on the penis itself;

and within the case thus formed, the corium had healed, and had become

pointed, but _inverted_; I presume that the point would, after another

exuviation, have been everted, and its length thus increased.

_Geographical Range and Habits._

With respect to range, the results arrived at have no particular

interest, for the species are not sufficiently numerous; and, what is

still more adverse, the genera, with unimportant exceptions, range over

the world; so that there is no scale of differences, and it cannot

be said that these two regions differ in their genera, and these two

only in their species. In all the following remarks, I have trusted

exclusively to my own specific identification; and have rejected all

assigned localities which appeared from any cause to be doubtful.

Sessile cirripedes are found in every sea, from lat. 74° 18′ north to

Cape Horn. The area included between the north point of the Philippine

Archipelago and the south point of Australia, extending on the right

hand to New Zealand, and on the left to Sumatra,--an area, which,

though including two distinct Cirripedial regions, is small compared

with the surface of the globe, yet includes a greater number of

species, especially of peculiar species, than the whole rest of the

known world. This is, probably, in chief part due to the broken nature

of the land, affording diversified habitats, and to much of the coast

being rocky. Cirripedes, from requiring to be attached, cannot live

where the shores and adjoining bottom are sandy or muddy or formed

of moving shingle; hence, no doubt, it arises, that there is such a

remarkable contrast in the great number of the species inhabiting

the bold rocky western coast of South America, and the few species

living on the sloping, and often sandy or muddy or shingly, eastern

shores of this continent. Hence, also, I believe, it is that not many

species have been brought from India. Coral-reefs are not favorable to

Cirripedes, consequently but few are known to inhabit the islands of

the Pacific Ocean. Where Cirripedes can live, though the species in no

district are numerous, the individuals abound in infinite numbers: I

have walked over the coast-rocks of the Falkland and Chonos Islands,

of Chile and Van Diemen's Land, fairly encrusted over wide spaces with

a continuous layer of Cirripedes, consisting of only two or three

species; in the same manner as may be observed on many parts of the

shores of Great Britain, and, I believe, of North America.

With respect to the effects of temperature on the range of Cirripedes,

no genus (having more than one species) is confined to the torrid

zones. Pyrgoma, from being always attached to corals, is, of course,

ordinarily found in the hotter seas; but one species ranges from the

Cape de Verde Islands in the torrid zone to the southern shores of

England and Ireland. Tetraclita is not found in the colder seas, but

is numerous in species and in individuals, on the southern shores of

Australia and at the Cape of Good Hope. I may here add, that the two

genera with the most confined ranges, are Chamæsipho and Elminius;

the former has only two species, one inhabiting Australia, and the

other the East Indian Archipelago; Elminius has four species, confined

to the southern hemisphere, and inhabiting Australia, New Zealand,

and South America. To return to the effects of temperature; in Mr.

Dana's great work on Crustacea, an excellent chart is given, in which

the _isocrymal_ lines, or those exhibiting the mean temperature of

the waters along their course, for the coldest thirty consecutive

days in any season of the year, are given; and which lines Mr. Dana

has shown are the most influential in governing the distribution of

marine animals. At the isocryme of 68°, Mr. Dana divides the torrid

and sub-torrid zones from the several temperate zones; and at 44°, the

temperate from the sub-frigid and frigid zones; but as no Cirripedes

are exclusively confined to these frigid zones, we may here disregard

them. From Mr. Dana's[76] table of the areas of the torrid and

temperate ocean-zones, on both sides of the equator, it seems that

they are nearly as 337 to 278, in relative area; and consequently, he

remarks, that the marine species in any class, if distributed equally

over the two, would be one fifth more numerous in the torrid than in

the temperate zones. Now of Cirripedes, taking all the orders, there

are at present known 147 species; of these, 7 have doubtful habitats,

leaving 140 for comparison. Of these 140, nearly one quarter, or

37, inhabit both the torrid and temperate zones, as above defined;

46 are found exclusively in the torrid, and 57 exclusively in the

temperate zones; so that the temperate zones, though less in area,

and having, proportionally, even a considerably lesser length of

coastline, nevertheless have a preponderance in the number of species.

But it should be borne in mind, that there are _two_ great temperate

districts, separated from each other by _one_ great torrid district;

and, inasmuch as the number of species in any region seems to depend in

some degree on the isolation of the sub-regions, we might have expected

(the other conditions now being, and the _past_ conditions having been

alike), that the two great temperate areas would have contained more

species, perhaps doubly more, than the single great torrid area.

[76] 'Crustacea: United States Exploring Expedition,' p. 1476

(corrected).

The proportional numbers, above given, are not very widely different,

whether we take separately the Balanidæ, the Lepadidæ, or all

together. Mr. Dana has shown[77] at length, that generally amongst

the Crustacea, the species which he considers of highest rank, belong

to the extra-torrid zones: there seems to me in all such cases to

be some degree of vagueness in the attempt to determine which are

highest or lowest, but I have already elsewhere stated that Balanus

is, probably, the most eminently Cirripedial form, and exhibits in the

strongest manner all the characters by which Cirripedes differ from

other Crustacea; as this genus is the largest, containing 36 species,

of which the habitats are known, I may state that of these, exactly one

third, or 12, inhabit both zones; 9 exclusively inhabiting the torrid,

and 15 exclusively the temperate zones. According to the proportions of

the whole class, the numbers should have been 9 torrid, to only 11.11

temperate; so that evidently the genus Balanus (in one sense typical)

inclines towards the temperate regions more strongly than does either

the family or the sub-class to which it belongs.

[77] Ibid., p. 1528.

With respect to the relation between the size acquired by the different

species of sessile cirripedes, and the temperature of the localities

inhabited by them, the genera Chthamalus, Tetraclita, and Balanus,

alone can serve for comparison: in Chthamalus much the largest species

is found in the temperate zone: on the other hand, the two largest

species of Tetraclita are from the torrid zone, though one of them

also sometimes ranges into the temperate seas: in Balanus, the largest

species, and six other species having a basal diameter sometimes over

two inches, inhabit the temperate regions; and two out of these seven

species, flourish even in the Arctic seas; whereas, within the torrid

zone, there are only three species with a diameter sometimes exceeding

two inches, but two of these frequently become very large and massive;

so that Balanus, judging from the size of the species, as well as

from their range, does not require for its highest development the

temperature of the torrid zones.

The greater number of the species of the Balanidæ have wide ranges, as

might be inferred from the fact of between one third and one fourth

of the total number inhabiting both the torrid and temperate zones;

but it should not be overlooked, that those species, as _Balanus

tintinnabulum_, _amphitrite_, _improvisus_, and, in a lesser degree,

_B. trigonus_ and _Tetraclita radiata_, which seem to range over

nearly the whole world (excepting the colder seas), are species which

are habitually attached to ships, and which could hardly fail to be

widely transported. Indeed, it appears to me surprising, that such

species as _Balanus psittacus_ and _eburneus_, which often become

attached to vessels, should still be confined, the one to Southern,

and the other to Northern America. But some other Cirripedes, which

I have never seen attached to vessels, have likewise immense ranges:

thus _Tetraclita porosa_ is found in every tropical and warmer sea,

and _Chthamalus stellatus_ ranges round the world in the northern

hemisphere, and, along the eastern side of America, far south of the

equator: _Balanus spongicola_, and _Acasta spongites_, extend from the

shores of Britain to the Cape of Good Hope: _Balanus lævis_ ranges from

Tierra del Fuego to California. I may further remark, that the only two

other species of Balanus, and the one Chthamalus, inhabiting Tierra

del Fuego, are, also, found on the shores of Peru. But to show the

powers of endurance in some species, I may specify the case of _Balanus

improvisus_, which flourishes on the coast of Nova Scotia, amongst

the West Indian Islands, in Southern Patagonia, and near Guayaquil.

Even more striking is the case of _B. crenatus_, of which I have seen

specimens from latitude 74° 48′ north, from the West Indies, and the

Cape of Good Hope! In these two latter localities, however, it seems to

be rare, and may have been first transported to them from the shores of

Europe, on the bottoms of vessels, to which it sometimes adheres.

The several species of Balanidæ live attached either to coast-rocks,

or to objects at various depths, down to, as in the case of _Balanus

crenatus_, 50 fathoms. _Balanus balanoides_ sometimes adheres to rocks

or wood so high up, that it is not covered by water during the neap

tides. Mr. Thompson has informed me, that he once accidentally kept

some specimens of this species out of water for seven days in a warm

room, and that they were then quite lively. This species, is very

easily killed by brackish water, as are some other species, whilst _B.

improvisus_ and _eburneus_ can flourish in it; and at the Falkland

Islands, I saw _Elminius Kingii_ attached to rocks at the mouth of

a fresh-water brook, so as to be covered by pure water during the

ebb of each tide. Sessile cirripedes adhere to all sorts of objects,

floating and fixed, animal and vegetable, living and dead, organic and

inorganic. Chthamalus is, perhaps, more commonly attached to rocks than

are the other genera. Living Mollusca are, I think, the most frequent

objects of attachment: Mr. Cuming has remarked to me, that shells

covered by an epidermis, as Patella, Haliotis, and Mytilus, are the

greatest favorites. Acasta is always imbedded in sponges, or in the

sponge-like bark of Isis; Pyrgoma and Creusia in corals; Chelonobia is

attached to turtles, and one species to crabs or very smooth shells;

Coronula, Tubicinella, and Xenobalanus, are imbedded in the skin of

Cetaceans; and Platylepas in that of manatee, turtles, or sea-snakes.

If we attempt, with our present not very imperfect materials, to

divide the globe into provinces, according to the amount of difference

in their Cirripedial inhabitants, including all orders and families,

and disregarding entirely, as I think we ought, all probabilities or

conclusions deduced from the distribution of other tribes of animals,

we find that the globe may be divided into the four following great

provinces and one sub-province. I should premise, that in the following

remarks and tables,[78] the species of Lepas, Conchoderma, Chelonobia,

Coronula, Platylepas, and Tubicinella, are excluded, owing to their

being attached to floating or swimming objects, and being consequently

widely and irregularly distributed.

[78] As the number of Cirripedes in the whole class is not very

great, I have given lists of the species in the four main provinces

and in the one sub-province.

The first, or North Atlantic province, is that of Europe and the

eastern shores of North America, from the arctic regions to lat. 30°:

the island of Madeira, part of the north-west coast of Africa, and the

whole Mediterranean being included. In this province (the above-named

genera being excluded) we have 31 species, of which 22 are not found in

any other distant quarter of the globe. As some few of these species

range into the West Indies, I have not, on this account, excluded them

from the 22 peculiar forms. Had I included the West Indies[79] in my

first province, the total number of species would have been 42, of

which 28 would have been peculiar. The coast of Brazil, even as far

south as the Rio Plata, might, also, have been included, for I have not

seen from it a single species not included in the above 42 West Indian

species. So also, by adding a single species, might the west coast of

equatorial Africa. The two coasts of South America and Africa, which

face each other within the torrid zone, seem to be remarkably barren

in Cirripedes. Europe has several more species than the United States,

which is inhabited by only ten species, including even the probably

imported _Balanus tintinnabulum_ and _amphitrite_. Of these ten United

States species only two are not found in Europe; and both these two

range into the West Indies, and as far as the northern shores of South

America, and therefore cannot be considered as peculiar to the United

States.

[79] The total number of species which I have seen from the West

Indies, is 19 or 20; of these, only 6 are peculiar to it, or 8, if

the United States be likewise included, the other 12 or 14 species

being found in other quarters of the world. Six peculiar species

out of 19 or 20, has not appeared to me sufficient to institute

even a sub-province.

I have formed my single sub-province for the southern extremity of

Africa; for although I know of only 11 species from this comparatively

short and uniform line of coast, yet I was not able to group these

eleven in any of the main provinces: 5 of the species are peculiar,

1 Australian, 3 European and West Indian, and 2 almost universally

distributed.

The second province includes the west coast of North and South America,

from Tierra del Fuego to Behring's Straits: on this enormously long

line of coast, only 22 species are known to exist, but of these no

less than 15 are peculiar. Of these 15, four are not found south of

the torrid equatorial region, and eight are not known to occur north

of this same region; so that this long line of coast might have been

divided into two sub-provinces, of which the southern would have been

the most peculiar; but as eight species are found both north and south

of the equatorial region, I have not made this sub-division. Two of

the species occurring on the western coast of North America, seem to

represent species found on its eastern coast, and in Europe; thus,

_Balanus glandula_ takes the places of _B. crenatus_, and _B. cariosus_

that of _B. balanoides_. Not a single species, excepting a few which

are also widely distributed over other parts of the world, is known to

be common to the east and west coasts of the two Americas.

The third province is that of the East Indian Archipelago, and includes

the Philippines, Borneo, New Guinea, Sumatra, Java, Malacca, and the

eastern coast of India. Here we find 37 species, of which 24 are

peculiar. I may remark, that I have received no species from Madagascar

or the eastern coast of Africa; few from India, or from the coast of

China; and I suspect, that on most of these coasts, only few exist.

Probably our third province will hereafter be found to include the

whole Indian Ocean.

The fourth province is that of Australia, including New Zealand: it

has 30 species, of which 21 are peculiar. Had the temperate Australian

coasts (_i. e._, those south of the isocryme of 68°) been alone

considered, the number of the species would have been probably 25, of

which 20 would have been peculiar,--that is, if we admit within the

20, several species which range from the temperate into the torrid

zone, but do not extend beyond the Australian shores. Owing to the

widely-extended ranges of most Cirripedes, no Arctic or Antarctic

provinces can be said to exist.

To recapitulate the above results, bearing in mind that, although the

total number of known existing Cirripedes is 147, yet that the habitats

of seven are unknown, and that eighteen are excluded owing to their

being attached to floating or swimming objects, so that there are only

122 species referred to in the following table:

+--------------------------------------------------+--------+---------+

| | Total | Species |

| | number |confined |

| | of | to the |

| |species.|province.|

+--------------------------------------------------+--------+---------+

|(1.) First, or North Atlantic Province, to lat. }| | |

| 30° N. (If the West Indies had been included}| 31 | 22 |

| the numbers would have been 42 and 28) }| | |

|(2.) Sub-province of South Africa | 11 | 5 |

|(3.) Second province, or West Coast of North and }| | |

| South America }| 22 | 15 |

|(4.) Third province, or East Indian Archipelago | 37 | 24 |

|(5.) Fourth, or Australian province | 30 | 21 |

+--------------------------------------------------+--------+---------+

The least prolific of these provinces contains 22 species, or between

1/5th and 1/6th of the total number of species, and the most prolific

between 1/3rd and 1/4th of this same number. In each of these

provinces, it is remarkable that the peculiar species are very nearly

two thirds of the whole of its inhabitants. These facts, I think, show

that the above provinces are natural divisions of the world, as far as

their Cirripedial inhabitants are concerned.

As Cirripedes belong to the great class of Crustacea, and as the

distribution of the latter has lately been fully discussed by Mr. Dana,

it may be worth while briefly to compare my results with his; more

especially as they are so very different. I should premise, as perhaps

accounting to a certain extent for this difference, that, owing to the

wide range of many species, and the almost universal extension of the

same genera, my provinces are founded merely on a certain proportion

of the species, namely, two thirds, being peculiar or confined to a

region of considerable dimensions: whereas, in the case of ordinary

Crustaceans, the greater number of the species are distinct even in

the sub-provinces, and the provinces are founded mainly on generic

differences. Mr. Dana divides the surface of the globe into three great

sections, or provinces, the _Africo-Europæan_, the extent of which is

shown by its title; the _Occidental_, which includes both the east and

west coast of both Americas; and the _Oriental_, including the Indian

and Pacific Oceans, with the East Indian Archipelago, and Australia.

Thus Mr. Dana entirely separates the Eastern shores of North America

from Europe; whereas, as far as their Cirripedial inhabitants are

concerned, they are most intimately allied, and form my first or North

Atlantic province; and to this, as I have shown, even the West Indies,

the coast of Brazil, and equatorial West Africa might have been added.

It follows, from this similarity in the Cirripedes on the two sides of

the Atlantic, and from their dissimilarity with those on the shores of

the Pacific, that the east and west coasts of the two Americas form two

quite distinct Cirripedial provinces; though, in the northern half,

some connection is shown by a few representative species: on the other

hand, Mr. Dana unites both sides of the whole American continent,

into his single Occidental province. The South-African province is not

brought out by Mr. Dana so prominently, as I have found necessary. Mr.

Dana joins the East Indian Archipelago and Australia into his single

Oriental province, and makes New Zealand, as a sub-province, apparently

as distinct from Australia, as Australia is from the East Indian

Archipelago: whereas I find that the Cirripedes of New Zealand clearly

belong to Australia; and that the Australian Cirripedes, especially if

the temperate shores be alone considered, are as distinct from those of

the East Indian Archipelago, as from those of any other quarter of the

whole world. I believe that the provinces deduced from the distribution

of Cirripedes, accord better with the Molluscan provinces, than with

those given by Mr. Dana for the rest of the great class of Crustaceans.

In the following tables, an asterisk means that the species is not

found in any other distinct region of the globe. When found in one

of the five provinces, a corresponding number, within brackets, is

appended, to show in which province or sub-province it has been found.

(1.) FIRST OR NORTH ATLANTIC PROVINCE: _Europe and the Eastern United

States, from the Arctic Regions to 30° north latitude._

Balanus tintinnabulum (1 to 5).

tulipiformis* confined to Europe.

calceolus Europe and India.

{ confined to North America and West

galeatus* { Indies.

spongicola (2) and West Indies (?).

{ confined to Europe, but possibly in the

perforatus* { West Indies.

amphitrite (1 to 5).

eburneus* { confined to North America and West

{ Indies.

improvisus Europe and North America and (3).

porcatus* Europe and North America.

crenatus " " W. Indies and (2).

balanoides* " "

Hameri* " "

Acasta spongites Europe and (2).

cyathus* Madeira and West Indies.

{ confined to Europe, but ranges as far at

Pyrgoma anglicum* { least as the Cape de Verde Islands.

Xenobalanus globicipitis* confined to Europe.

Chthamalus stellatus Europe and North America and (3 and 4).

Pachylasma giganteum* confined to Europe.

Verruca Strömia Europe and Red Sea.

Spengleri* Madeira.

Pœcilasma aurantia* "

crassa* "

Dichelaspis Lowei* "

Oxynaspis celata* "

Alepas minuta* Europe.

parasita* Europe and Atlantic Ocean.

Anelasma squalicola* Europe.

Alcippe lampas* "

Scalpellum vulgare* "

Pollicipes cornucopia* "

Here we have 31 species, of which 22 are not found in any other great

region of the world.

(2.) SUB-PROVINCE: _Africa, South of lat. 30°._

Balanus tintinnabulum (1 to 5).

Capensis*

spongicola (1) and West Indies (?).

amphitrite (1 to 5).

crenatus (1) and West Indies.

Acasta spongites (1).

Tetraclita serrata*

rosea (4).

Chthamalus dentatus* also on West Coast of Africa.

Octomeris angulosa*

Scalpellum ornatum*

In this small region we have only 11 species, of which five are

peculiar: _Balanus Capensis_ and _Tetraclita serrata_, seem to be

representatives of _B. psittacus_ of S. America and of _T. porosa_ of

that and several other regions.

(3.) SECOND PROVINCE: _West Coast of South and North America, from

Tierra del Fuego to Behring's Straits._

Balanus tintinnabulum north and south of the equator (1 to 5).

psittacus* south.

vinaceus* "

trigonus north and south (4 and 5).

lævis* "

concavus " (4 and 5).

pœcilus* south.

improvisus south (and north?) (1).

nubilus* north.

glandula north, and Southern Pacific Ocean.

cariosus* north.

Tetraclita porosa north and south (4 and 5 and W. Indies).

Elminius Kingii* south.

Chthamalus stellatus north.

cirratus* south.

scabrosus* "

fissus* north and south.

Hembeli* north.

Verruca lævigata* south.

Pollicipes elegans* south and north.

polymerus* "

Cryptophialus minutus* south.

Here we have on this long line of coast, 22 species, of which 15 are

peculiar.

(4.) THIRD PROVINCE: _Indian Archipelago (including the Philippines,

Malacca, Borneo, Sumatra, Java, and New Guinea, and eastern coast

of India)._

Balanus tintinnabulum (1 to 5).

Ajax*

navicula*

stultus and West Indies.

trigonus (3 and 5).

concavus (3 and 5).

amphitrite (1 to 5).

patellaris*

amaryllis (5).

quadrivittatus*

Acasta lævigata and Red Sea.

fenestrata*

purpurata*

sporillus*

Tetraclita porosa (3 and 5) and West Indies.

costata*

vitiata (5).

cœrulescens Pacific Ocean.

radiata (5) and West Indies.

Pyrgoma cancellatum*

grande*

milleporæ*

crenatum*

monticulariæ*

Creusia spinulosa and West Indies.

Chthamalus stellatus (1 and 3).

intertextus*

Chamæsipho scutelliformis*

Octomeris brunnea

Pœcilasma fissa*

eburnea*

Dichelaspis Warwickii*

Ibla Cumingii*

Scalpellum rostratum*

Pollicipes mitella*

Lithotrya Nicobarica*

truncata and Pacific Ocean.

Here we have 37 species, of which 24 are peculiar to this province.

(5.) FOURTH PROVINCE: _Australia (including New Zealand)._

Balanus tintinnabulum (1 to 5).

nigrescens*

decorus*

trigonus (3 and 4).

concavus (3 and 4).

amphitrite (1 to 5).

amaryllis (4).

allium*

vestitus*

imperator*

Acasta sulcata*

glans*

Tetraclita porosa (3 and 4).

rosea (2).

purpurascens*

vitiata (4).

radiata (4) and West Indies.

Elminius plicatus*

simplex*

modestus*

Chthamalus antennatus*

Chamæsipho columna* and Pacific Ocean (?).

Pachylasma aurantiacum*

Catophragmus polymerus*

Alepas tubulosa*

Ibla quadrivalvis*

Scalpellum Peronii*

Pollicipes spinosus*

sertus*

Lithotrya cauta*

Here we have 30 species, of which 21 are peculiar.

_Geological History._

The ancient history of the Balanidæ is a brief one. No secondary

species has hitherto been discovered; in my monograph on the fossil

Lepadidæ[80] I have shown that the negative evidence in this case is of

considerable value, and consequently that there is much reason to doubt

whether any member of the family did exist before the Eocene period.

The existence of a Cretaceous Verruca is an apparent exception to the

rule, as this genus has hitherto always been ranked amongst sessile

cirripedes; but Verruca, as we now know, must be placed in a family by

itself, quite distinct from the Balanidæ. Balanus is the oldest genus

as yet known; it first appeared in Europe and North America, during

the deposition of the eocene beds; and was at that time, as far as our

information at present serves, represented by very few species. In

South America, one species of Balanus abounds in individuals in the

ancient Patagonian tertiary formation. I have seen, in the British

Museum, specimens, said to have come from the eocene nummulitic beds

near the mouth of the Indus, belonging to the second section of the

genus. Generally, the extinct forms belong to the last section of

this genus, which has the parietes not permeated by pores. During the

miocene and pliocene ages, sessile cirripedes abounded. No extinct

genus in this family has hitherto been discovered. It is singular,

that though the Chthamalinæ approach much more closely than do the

Balaninæ to the ancient Lepadidæ, of which so many species have been

found fossil even in the older Secondary formations, yet that only one

species of one genus of this sub-family has been hitherto found in any

deposit; and that species is the still existing _Pachylasma giganteum_,

in the modern beds of Sicily. During the epoch of the Glacial deposits

in Scandinavia, Scotland, and Canada, the still existing species seem

to have abounded; and they attained larger average dimensions than

the same species now do on the shores of Great Britain, or even on the

shores of the northern United States, where the average size seems

larger than on this side of the Atlantic.

[80] Since the note to page 5 of that work was written, I have been

informed that the so-called cretaceous _Tubicinella maxima_ is not

a Cirripede.

Under the genus Balanus, I have given my reasons for never naming

species in this large and difficult genus, without examining the

opercular valves: it has been owing to this, as it appears to me,

proper want of caution, that there are so many nominal species. Thus

it is made to appear in catalogues, that the tertiary seas abounded

with species of Balanus to an extent now quite unparalleled in any

quarter of the world. Bronn,[81] for instance, in his invaluable

'Index Palæontologicus,' gives the names of 35 Balani, found fossil in

Europe, and I have not counted those found only in alluvial deposits,

as they would certainly be the same as the still living species. Now

I know only 11 recent Balani on the shores of all Europe, from the

North Pole to lat. 30°; and of these I doubt whether _B. balanoides_

and _improvisus_ have been found fossil. In the Red Crag there is one

extinct Balanus: in the Coralline Crag, which seems to have been very

favorable to the existence of Cirripedes, there are six species of

Balani, of which two are absolutely extinct, and one does not occur

in any neighbouring sea: in the Eocene formations the species seem to

have been rare, and I have seen only one, and that is an extinct form.

Taking these several facts into consideration, and bearing in mind

that Cirripedes usually range widely, I do not believe, if all the

specimens of Balani hitherto found in the several tertiary formations,

from the eocene to the glacial deposits, throughout Europe, were

collected together, they would amount to 20 species. I have myself

seen, in a recognisable state, only 12 fossil species, of which five

are extinct, or not found in any neighbouring sea: I think it probable

that three other recent species, viz. _B. tulipiformis_, _perforatus_,

and _amphitrite_, may occur in the Mediterranean formations; and this

would make 15 species. Therefore in the above estimate of 20 species,

five are allowed for species existing in European collections,

but not hitherto seen by me; and this, I believe, is a very full

allowance. Consequently, even on the supposition that the five

species just admitted as possibly existing in cabinets, and that the

other five extinct species, which I have seen and examined, have all

been previously named by other authors, a supposition excessively

improbable, even then there would be 15 superfluous names in Bronn.

[81] To save any other person, interested in fossil Cirripedia,

going through the several works quoted by Bronn, I have given some

remarks on his list of species, in an appendix at the end of the

Balanidæ.

The following short table shows how Cirripedes, including all three

Families, were represented in Great Britain, throughout the several

TERTIARY STAGES.

A = Living species but found fossil in some tertiary deposit.

B = Mammilliferous crag, and glacial deposits.

C = Red crag.

D = Coralline crag.

E = Eocene.

+----------------------------+---+---+---+---+---+

| Name. | A | B | C | D | E |

+----------------------------+---+---+---+---+---+

| Balanus tintinnabulum | * | | * | | |

| calceolus | * | | | * | |

| spongicola | * | | | * | |

| concavus | * | | * | * | |

| porcatus | * | * | * | | |

| crenatus | * | * | * | * | |

| Hameri | * | * | * | | |

| bisulcatus | | | * | * | |

| dolosus | | * | | | |

| inclusus | | | | * | |

| unguiformis | | | | | * |

| Acasta undulata | | | | * | |

| Pyrgoma anglicum | * | | | * | |

| Coronula barbara | | | * | | |

| Verruca Strömia | * | * | * | * | |

| Scalpellum magnum | | | | * | |

| quadratum | | | | | * |

| Pollicipes reflexus | | | | | * |

+----------------------------+---+---+---+---+---+

| Total, 18, recent and } | | | | | |

| extinct, found fossil in } | 9 | 5 | 8 |10 | 3 |

| Great Britain, in some } | | | | | |

| tertiary deposit } | | | | | |

+----------------------------+---+---+---+---+---+

As affording some standard of comparison by which to compare the number

of fossil species, at any period, in relation to the number of species

probably existing in the neighbouring seas during the same epoch, I

may state that there are now living and propagating on the shores of

Great Britain, 18 species belonging to the three Families included

in the above table. I have not counted three species, in the genera

Alcippe and Conchoderma, which, from the minuteness of their valves,

it is hardly possible would be found fossil. On the other hand, I have

included in the 18, five species of Lepas, which from floating and

being oceanic, are more likely to be cast up on beaches, than to be

imbedded in sedimentary deposits; so that 13 would, perhaps, be a safer

number, as a standard of comparison. Now in the coralline crag, which

seems to have been eminently favorable for the existence and subsequent

preservation of Cirripedes, and which has been so well worked, only

nine fossil species, as may be seen in the table, have been as yet

discovered.

Sub-Family--BALANINÆ.

_Shell with the rostrum having radii, but without alæ; lateral

compartments all having alæ on one side and radii on the other side;

parietes generally either porose, or longitudinally ribbed on their

inner surfaces._

_Mouth with the labrum notched in the middle, not swollen; palpi large,

almost touching each other; mandibles generally with the lower teeth

laterally double; third pair of cirri with their segments resembling

those of the second pair._

_First Section._†

_Scutum and tergum articulated together, or overlapping each other;

each branchia composed of a single plicated fold._

_Genera_--Balanus; Acasta; Elminius; Tetraclita; Pyrgoma; Creusia;

Chelonobia.

_Second Section._††

_Scutum and tergum (when both are present) not overlapping each other;

basis membranous; parietes often deeply folded, with the outer lamina,

towards the basis, generally imperfect; each branchia composed of two

plicated folds; shell attached to living vertebrata._

_Genera_--Coronula; Platylepas; Tubicinella; Xenobalanus.[82]

[82] At the end of the volume a Synopsis is given, which will serve

as a systematic index for the discovery of generic and specific

names.

The Balanidæ may be divided into two sub-families; namely, the Balaninæ

and Chthamalinæ; and, in the former, the genera, as we see, may be

very naturally grouped into two sections. The Balaninæ differ from the

Chthamalinæ, as far as the shell is concerned, in the rostrum having

radii but no alæ, all the lateral compartments having both radii and

alæ; on the other hand, in the Chthamalinæ, the rostrum has alæ, and

the rostro-lateral compartments radii on both sides, and therefore

no alæ. These differences probably arise, as already explained, from

the perfect confluence, in the Balaninæ, of the true rostrum with the

rostro-lateral compartments. In Chelonobia, belonging to the Balaninæ,

we see an intermediate state, with the fusion not quite effected:

on the other hand, in one genus amongst the Chthamalinæ, namely,

Pachylasma, we must look to the shell at a very early age, to find the

rostrum with its alæ, distinct from the rostro-lateral compartments.

In Tetraclita, Elminius, and Creusia, the carino-lateral compartments

are aborted, or possibly confluent with the lateral compartments,

making altogether only four: in Pyrgoma all the compartments are

fused together and form a solid ring. The sub-genus Acasta is, in

one sense, very natural, as it includes species most closely allied:

in another sense it is far from natural, as some of the species can

hardly be distinguished from those species of Balanus, which live

attached to Gorgoniæ: I almost regret I did not merge the species of

Acasta into Balanus. In the Balaninæ generally the parietes are either

porose, or are furnished on their internal surfaces with regular ribs,

representing the longitudinal parietal septa, which in other species

form the tubes or pores; there are, however, many exceptions to this

rule in several species of Balanus, in Acasta and Elminius, all of

which have the parietes of their shells internally quite smooth, or

only irregularly roughened with points.

Looking to the animal's body, in the Balaninæ, the labrum is always

notched in the middle, and is never swollen or bullate, for the outer

and inner folds of membrane of which it is composed lie close together.

The palpi are large, so that their tips almost touch each other. The

mandibles, generally, have their lower main teeth laterally double.

Of the cirri, the third pair invariably much more closely resembles,

in its whole structure, and in its action, the second than the fourth

pairs; and it is also generally separated by a small interval from the

fourth pair.

I have already under the Family sufficiently entered on the relations

of the Balaninæ to the Chthamalinæ, and of the genera, one to the

other, so that I need not here add anything.

I can point out no difference in habits or geographical distribution

between the Balaninæ and Chthamalinæ.