ORDER II.--ABDOMINALIA.

_Cirripedia, having a flask-shaped carapace; body consisting of one

cephalic, seven thoracic, and three abdominal segments; the latter

bearing three pairs of cirri; the thoracic segments without limbs;

mouth with the labrum greatly produced, and capable of independent

movements; œsophagus armed with teeth at its lower end: larva, firstly

egg-like, without external limbs or an eye; lastly binocular, without

thoracic legs, but with abdominal appendages._

I feel compelled to form an Order for the one genus and species,

namely, _Cryptophialus minutus_, to be here described. We must, I

conceive, attribute much greater value, in classification, to internal

parts and organs, at least where such are not known to vary, than to

external structure. Now in Cryptophialus, the body consists of eight

segments, of which the first two are not developed in any cirripede

hitherto described. Of the eight, the seven posterior or thoracic

segments are quite free, or detached from the carapace, and do not

bear any appendages; whereas in all the foregoing cirripedes of the

order Thoracica there are (at least in the normal sex) six pairs of

cirri; Alcippe alone must be excepted, in which there are only two

pairs. Again, in the Thoracica there are no abdominal appendages,

excepting the terminal or caudal, whereas in Cryptophialus the abdomen

bears three pairs of biramous cirri. In the crest of the labrum,

being produced into a special, lancet-formed organ, articulated at its

base and capable of movement, and in the palpi projecting straight

upwards, we have a great difference from all other cirripedes;

and these organs, we have every reason to believe, possess a high

classificatory importance. The œsophagus in Cryptophialus, where it

enters the stomach, is armed with teeth and hairs, moved by muscles,

forming a beautiful structure, of which we have not a trace in any

other cirripede. Lastly, and perhaps most importantly of all, the

metamorphosis is different; for the early larval stages are passed

under an egg-like condition within the sack of the parent; and the pupa

differs from the pupæ of all other cirripedes, in not having natatory

thoracic limbs, and is therefore only able to crawl about by the aid of

its great prehensile antennæ.

Thus far the evidence is decisive in favour of Cryptophialus being

placed in a separate Order; but if we were to trust to the characters

derived from the external covering or carapace,--and such characters

are of high importance, as we may safely infer from the natural

arrangement of the foregoing families which depends on the structure

of the carapace,--we should place Cryptophialus close to Alcippe

amongst the Lepadidæ. These genera agree in their burrowing habits,--in

their attachment by a horny rostral disc,--in the external membrane

being covered with triturating points,--in the spinose and notched

orifice, with an external lateral bar on each side, and in the inner

tunic of the sack being protected by hairs and spines. They agree to

a considerable extent in shape, and in the peculiar arrangement of

the muscles of the whole external covering of the animal: they agree,

also, in their manner of growth, and in the sack extending down to

their basal extremity. Some of these resemblances may possibly be

analogical, and due to similarity of habits, and not to affinity; and

we must attribute to mere similarity in function, a certain amount of

resemblance in their labrums, for this part is essentially different

in the two genera; and to the same cause, the resemblance between the

brush formed by the two pairs of thoracic cirri and caudal appendages

at the end of part of the thorax in Alcippe, with the three pairs of

abdominal cirri at the end of the whole thorax in Cryptophialus. I

allude to this latter resemblance, for it was owing to it, and to the

similarity in the habits of Cryptophialus and Alcippe, that I stated,

in the introduction to my former volume on the Lepadidæ, that the two

genera would probably fall into the same order. In the structure of all

the parts of the mouth and of the cirri, in the digestive organs and in

the metamorphoses, Cryptophialus is not more closely related to Alcippe

than to any other genus whatever amongst the Lepadidæ.

Nevertheless I am confirmed in the view that the external resemblances

between these two genera are due to some real affinity, and are not

merely analogical, by a very remarkable fact,--namely, that Alcippe and

Cryptophialus are both bisexual, and have males, several in number,

attached exactly in the same position, and which males are so closely

similar that, considered by themselves, they might absolutely be almost

classed as species of the same genus! For they agree in the absence of

all internal organs and parts, excepting the single testis, vesicula

seminalis, and immensely long probosciformed penis; and they agree,

also in manner of growth, in the arrangement of the muscles, and even

in shape. The whole case seems to me very singular, and, as far as my

knowledge extends, unique: we have two animals, of which the females,

if classed by their external parts (homologically consisting of the

three anterior segments of the head), would be placed alongside each

other in the same family; but when classed by the whole rest of their

organisation, certainly must be ranked in distinct orders;[150] yet

the males of these very same animals might almost stand in the same

genus. If it be asked why the position of Cryptophialus in the system

should not be determined by the male, instead of by the female, the

answer would be that the male is here abnormal and rudimentary in

its whole structure; and I believe systematists are agreed that less

perfect parts (and therefore a less perfect whole) offer less valuable

characters than the more perfect parts or whole. We see this conclusion

plainly verified in the case of the hermaphrodite _Scalpellum vulgare_

and _Ibla quadrivalvis_, for there can be no doubt where these species

should be arranged, yet if we attempted to place them by their

complemental males, we should utterly fail: exactly in the same manner,

if _Ibla Cumingii_ and _Scalpellum ornatum_ were ranked by their males,

they would be quite misplaced. So again, if we were to attempt to class

the six species of Scalpellum by their males and complemental males,

undoubtedly the first three and last three species of the genus would

have to stand in distinct orders! Hence we may reject the males as a

foundation for classification, but no doubt they serve to show that the

resemblances in the carapaces of Alcippe and Cryptophialus, are not

merely analogical or functional, but evince a true affinity, though

these genera differ so greatly, in mouth, body, œsophagus, cirri, and

especially in their metamorphoses.

[150] M. Milne Edwards would, perhaps, in accordance with the

profound views lately propounded by him on classification, consider

Cryptophialus as an extremely modified, and, to a certain extent,

degraded member or satellite of the _type_ of the Lepadidæ; but

I do not myself feel able to draw a line of distinction between

the being a very abnormal member of one group, and belonging to

a distinct group. I may add that I have several times tried to

persuade myself, with no success, into the belief that I have

somehow misunderstood the homologies of the thoracic segments and

cirri of Alcippe and Cryptophialus; for if this were so, the two

genera could be brought into much closer relationship; but with

any conceivable amount of error on my part, there remains the

great difference in the metamorphosis, not to mention the palpable

differences in the cirri, the parts of the mouth, and in the whole

course of the alimentary canal.

CRYPTOPHIALUS MINUTUS. Pl. 23, 24, fig. 1 to 19.

_Hab._--Chonos Archipelago, Southern Chile; imbedded in the

_Concholepas Peruviana_.

FEMALE. Fig. 1-18.

_General Appearance._[151]--This, the smallest known cirripede, is

flask-shaped and compressed, with a small orifice, on a more or less

produced neck, placed at one corner: one of the narrow sides of this

carapace is somewhat flattened or depressed, with its superior edge

prolonged a little upwards; by this side, the animal is attached to

the cavity in the shell, within which it is lodged. There is here no

distinction between a peduncle and capitulum, that is between the

lower or anterior, and the upper or posterior end of the animal,

as seen externally. The small orifice is toothed and hairy: it is

coloured purple, as is likewise the projecting labrum; the rest of

the animal being tinted only by the muscles and internal parts seen

through the outer integuments. The largest specimen (fig. 2) which I

have measured did not quite attain the length of one tenth of an inch.

This cirripede inhabits, in vast numbers, the shells of the living

Concholepas Peruviana, amongst the Chonos islands; the whole outside

of the shell being sometimes completely drilled by its cavities,

almost touching each other, as happens in the case of Alcippe with the

shells of Buccinum. The oval aperture leading into the shell-cavity,

in full-sized specimens, is between (2-3)/100 of an inch in length: it

is generally surrounded by a narrow, internal, calcareous rim, which

apparently has the same inorganic origin, as in Alcippe. The toothed

orifice of the carapace leading into the sack, fills up the orifice of

the shell-cavity; but it can be voluntarily withdrawn a little: when

opened, and the animal is in action, the lancet-formed, moveable crest

of the labrum, and the abdominal cirri, are exserted.

[151] I am greatly indebted to Dr. Hooker, for having several years

ago, when I examined this my first cirripede, aided me in many

ways, and shown me how to dissect the more difficult parts, and for

having made for me several very correct drawings, which, with some

subsequent alterations, are now engraved.

_Integuments._--The external membrane is colourless, thin, but strong;

it is studded with minute bifid, trifid, and quadrifid points of hard

chitine, which are the agents of excavation: they are directed upwards,

except towards the lower end, where they are directed from the disc

or surface of attachment. These points beneath the orifice, and on

each side close along the lateral bar, are larger than elsewhere.

There are no points on the disc or surface of attachment, which is

formed of somewhat thickened, yellowish membrane, and is not moulted,

like the rest of the external membrane, but is formed of successive

layers extending beyond each other; the lines of growth, however,

being obscure, and only occasionally distinguishable. The disc is

oval, not extending to the lower end of the animal, and with the upper

edge thinning out and produced upwards (fig. 1). The animal, during

its growth, moves a little downwards in its cavity, by means of the

new layers of the attached disc being formed, not symmetrically with

respect to the old layers, but beyond them or at a greater depth in

the shell; hence when the animal is removed quite perfect, by the

Concholepas being dissolved in acid, the upper and deserted margin

of the disc or surface of attachment generally projects as a free

edge, but in a tattered and worn condition. In full grown specimens,

which have ceased burrowing downwards, nearly the whole disc, though

occupying the same position relatively to the animal, becomes in fact

deserted, and is lined by membrane continuous with, and like that,

investing the rest of the body, but furnished only with simple blunt

points, instead of with the sharp bifid and trifid triturating points.

The orifice is formed on each side by a toothed rim of hard chitine

(fig. 3, 4), which can be opened and shut, owing to its being flexible

at the rostral end, and folded inwards at the carinal or posterior

end. The teeth vary in arrangement and sharpness: generally they form,

taking a rim on one side (fig. 3), two prominences or groups of points

at the rostral or anterior end, always separated by a broad notch,

from the bottom of which the lateral bar extends downwards, from the

posterior, larger and less regularly toothed half of the rim. Of these

teeth the larger ones project nearly straight up, and the smaller and

lower teeth outwards, graduating into the smaller teeth, just below

the rim, which again graduate into the minute points, studded over the

whole surface. These outer teeth probably serve to prevent any creature

crawling into the cavity, between the shell and animal. Scattered

bristles rise from all over the rim. The lateral bar, above alluded

to, consists of the general membrane of the body, thickened, hardened,

rendered elastic, coloured yellow, and apparently formed into a fold:

where attached to the under side of the rim, at the above-mentioned

notch, the bar is thinner and more flexible than elsewhere: it runs

half way down the animal, first straight and then curved towards

and closely approaching the disc or surface of attachment. At the

lower end, the bar, or more strictly the thickened membranous margin

of the bar (_b′_, fig. 3), expands into an oblong, slightly rigid

plate, studded with from three or four to ten or twelve points, which

have their ends expanded and truncated, or even slightly bifid. The

extremity of this plate projects freely from the general surface of the

body. We shall afterwards refer to the use of this extremely peculiar

bar and plate.

The two rims forming the orifice cannot be quite closed; but ingress

by any foreign object into the sack is beautifully prevented by an

internal membranous lip on each side (_d′_, fig. 3, 4), and by a

third inwardly folded lip (_d′_) at the posterior and broad end of

the orifice. These three lips can be brought together, and form a

valve. The lateral lips are very narrow at the mouth or rostral end

of the orifice, where the hairy lancet-shaped crest of the labrum

closes the orifice, and largely expand towards the posterior end: they

are produced from the inner tunic of the sack: they appear formed of

the finest hairs, placed parallel and approximate, but when examined

under the highest powers, these hairs (for they still appear such) are

found to be united by delicate membrane, which has its extreme edge

fimbriated. The third, or posterior and inwardly folded lip, differs

in being composed of much coarser, flattened hairs, which are united

towards their bases, and are free at their extremities, where they are

serrated or coarsely plumose on both sides.

The sack extends down to the lower end of the animal. It is lined by

delicate membrane. At the orifice on each side, a little posteriorly

to the lateral external bars, this inner membrane is strengthened by a

pair of thin yellowish bars (_c′_, fig. 3), which run parallel to the

straight portions of the external bars. These inner bars at their lower

ends become pointed and die out: at their upper ends, and close to the

rim, they are broader, but more flexible, and so transparent as hardly

to be distinguished from the rest of the membrane. At the rostral end

of the orifice, in a medial line, this same inner tunic of the sack

is thickened for a short space downwards, so as to form a fifth bar

(_c′′_); which separating from the inner tunic, runs inwards between

the outer and inner membranes of the carapace (_i. e._ between _b_ and

_c_, fig. 3, 5), behind the mouth, as far down as opposite to the lower

end of the œsophagus, and there becoming thinner and ligamentous,

gives attachment to some powerful muscles.

At each exuviation, the external membrane with the dentated hardened

orifice, the lateral bars, the inner tunic of the sack with its bars,

are all moulted, together with the usual integuments of the animal's

body. New and sharp triturating points are thus periodically formed for

the work of excavation. The whole animal increases during growth in

every direction, and therefore, at its lower or basal end, as was the

case with Alcippe. The disc or surface of attachment, is added to by

new underlying layers, extending beyond the old layers at the lower end

and on the sides, but not at the upper end, where, as in the case of

the calcareous discs of Lithotrya, the old layers are deserted and worn

away. I saw what I believed to be little globules or patches of cement;

but I was not able to discover any cement-ducts.

_Muscles of Sack and Orifice._--The animal is surrounded by rather

strong longitudinal muscles, not running up close to the orifice: these

muscles exhibited, to my surprise, distinct traces of transverse striæ:

there are no external transverse muscles, as in all the Lepadidæ.

Attached to both sides of the inward fold or hinge, at the posterior

end of the orifice, some striated or voluntary muscles run for a short

distance downwards, diverging like a fan: their contraction would cause

the dentated rim to open: a strictly homologous muscle occurs only in

Alcippe. At the opposite end of the orifice, a remarkably powerful

voluntary muscle is attached to the ligamentous bar above described as

proceeding from the rostro-medial end of the toothed rim (_c′′_); and

at its lower expanded end, it is attached under rather above the middle

of the disc: this muscle corresponds with a similar one in Alcippe,

and with some much weaker muscles in other Lepadidæ. Its action would

be to draw down within the shell-cavity the whole dentated rim, and

likewise to close the orifice; and here, I believe, come into use

the lateral elastic horny bars with their curious basal projecting

plates, furnished with expanded points, for much friction would thus

be caused by, yet some play be allowed for, the several movements;

the elasticity of the bar bringing up the dentated orifice, when the

powerful muscles attached to the rostral end of the latter became

relaxed. Round the space where the just-mentioned muscles are attached

to the horny disc, a sheet of other muscles radiate, a few on both

sides obliquely upwards, but the greater number transversely and within

the first-described longitudinal muscles; they extend on both sides

about half round the animal. There are similar muscles in Alcippe, but

not extending so far round the animal. Their action must be to draw the

whole carapace towards the surface of attachment; the action of the

longitudinal muscles being to shorten it; the orifice supported by the

lateral horny bars, serving as the fulcrum for the contraction of the

longitudinal muscles. I could not see any adductor scutorum muscle,

although I looked particularly under the expanded plates at the ends of

the lateral external horny bars.

_Body._--This is laterally compressed: it is widest and thickest at the

upper end, and thence tapers to the lower or posterior end. The last

three or four thoracic segments are bent under the anterior segments,

giving the whole something of the appearance of certain crustaceans,

divested of their legs. The somewhat conical mouth, with its singular

labrum, is very large. The body consists of eight segments. The first

segment (fig. 5, 1), or that succeeding the mouth, is the seventh or

last cephalic segment of the archetype crustacean; it is the largest of

all eight segments; it is joined by its dorsal surface to the carapace

or external covering of the animal, and the membrane with which it is

invested is prolonged upwards and downwards (_c_, _c_, fig. 5), and so

forms the inner tunic of the sack. The succeeding seven segments are

thoracic; they are free, and are destitute of limbs; the articulations

separating them are transverse. The first and second thoracic segments

give rise, on their medial dorsal surfaces, each to a remarkable

tapering curved appendage, presently to be described. At the end of the

last thoracic segment, there is a minute abdomen, bearing three pairs

of biramous cirri.

The _Mouth_ consists of three pairs of organs, namely, the outer

maxillæ, maxillæ, mandibles with their palpi, and of a great and very

curious labrum. These organs, by the fusion (as in other cirripedes)

of their lower segments, form a large, somewhat conical, projecting

mouth, which is separated on the ventral surface from the rest of the

body by a distinct fold or articulation, where the muscles proceeding

to the above gnathites are attached. The labrum (_e_, fig. 5, 9) is of

large size; and the crest close over the opening of the œsophagus is

produced into a great, lancet-shaped, moveable organ, wholly unlike

anything occurring in any other cirripede: it is coloured purple, and

is thickly fringed in the upper part by very fine hairs: it is bowed a

little backwards from the mouth: the base, which rather overhangs the

œsophagus, is a little contracted, and is transversely marked by an

articulation: two small, parallel, voluntary muscles (with transverse

striæ) are attached at their lower ends close beneath the articulation,

and extend about one third up the organ: their contraction would serve

to erect it; and their relaxation would, apparently, allow it to fall

backwards on a little knob (_e′_, fig. 5) behind. This little knob

resembles a similar projection in many of the Lepadidæ. As the labrum

is formed of similar membrane with that of the succeeding segment of

the body, its limit downward, beneath the knob, can be told only by a

small apodeme which projects inwards, at a little distance within the

line where the membrane of the body is reflexed upwards (_c_), so as to

form the inner tunic of the sack.

The mandibles, palpi, and maxillæ, all project more than is usual. The

_Palpi_ (_f_, fig. 9, 5) are narrow, flattened, and taper a little;

they support a few long bristles on their tips, and on one of their

sides. In every other cirripede (in which the palpi are developed) they

are directed transversely across the mouth, one towards the other, and

are for a considerable space united to the labrum: here they project

straight up, and seem to rise exteriorly to the bases of the mandibles;

they are, however, united to the basal lateral edges of the labrum, and

when the latter is torn from the rest of the mouth, the palpi separate

with it. I could not distinguish the knob on which, in every other

cirripede, the palpi are articulated. The _Mandibles_ (fig. 8) have an

upper, lower, and middle tooth, with some finer intermediate points

and hairs. The _Maxillæ_ (fig. 7) are narrowed in at their spinose

edge, where there are three large spines and several finer bristles,

together forming a flattened brush: this organ is remarkable from the

apodeme (_a_) being bent into the shape of a scythe, with the terminal

or blade-portion a little expanded, and directed backwards and inwards.

The _Outer maxillæ_ are sub-triangular in outline, with several

bristles on their summits and along their outer surfaces.

_Segments of Body._--I have stated that the mouth is succeeded by

eight segments. As in all the cirripedes hitherto described, the

body consists of only six segments, the number eight at first seems

very improbable, and therefore I may be permitted to state that both

Dr. Hooker and myself, when first examining this animal, and having

no notion whatever regarding its homologies or the structure of

other cirripedes, came to the conclusion, judging only from external

appearances, that is, from the transverse folds, and from the lines of

movement when the body was bent by a needle, that there were really

eight segments. I have since carefully looked to this point: when the

outer membrane is cleaned and examined, the four posterior segments are

very plain, owing to a dorsal medial line, being alternately either

thickened and coloured yellowish, or thin and colourless: the four

anterior segments are less plain, but yet the membrane on the dorsal

surface, on the line of each fold or articulation, does present some

difference, from being destitute of the fine, transverse, toothed

scales which occur on other parts. But I lay most stress on the fact,

that all these eight articulations were used for the attachment of

muscles. Hence I conclude that the eight segments are real; and we

shall see, in the next order, that the very same eight segments are as

plain in Proteolepas, as in the larva of an insect or as in an annelid.

There is good reason to believe that the general covering or carapace

consists in all cirripedes of the three anterior segments, and that the

mouth (judging from its appendages) also consists of three segments,

consequently the first segment of the body in Cryptophialus must be the

seventh or last cephalic segment, and the seven next free segments must

be the normal seven thoracic segments.

The first segment of the body (_i. e._ last cephalic, fig. 5, 1) is,

as stated, the largest, and is attached dorsally to the carapace:

its ventral surface is flattened, and is formed of somewhat thickened

membrane: on each side, a little below the articulation separating this

segment from the mouth, there is a small blunt projection, with the

free part only 1/500th of an inch in length. Each of these appendages

bears four or five bristles on one side near the summit, and a few

on the other side, lower down: from their position I believe them

to be rudiments of a first pair of maxillipeds (tetartognathites of

Milne Edwards), of which no trace occurs in any other cirripede. The

differences between this segment and the seven succeeding segments,

is of interest, as offering some confirmation of the belief, lately

disputed by some naturalists, that the cephalic and thoracic segments

in the class Crustacea, do differ in their nature,--a conclusion which

we shall see further confirmed under Proteolepas. The second and third

(_i. e._ first and second thoracic) segments (2, 3, fig. 5) are the

next largest, and are remarkable from supporting singular appendages,

already alluded to. The sides of the second segment are formed of

thickened yellowish membrane. The fifth and sixth segments are the

smallest, and mark the point of chief flexure of the body. The eighth

segment is a little elongated, formed of thicker membrane than the

other segments, and dorsally is indented by the anus.

The singular tapering appendages (fig. 5, _i_, _k_) arising dorsally

from the second and third segments, differ from each other only by the

upper one being smaller, less curled, and perhaps rather smoother. When

first examining this animal, not knowing that it was female, and not

finding a probosciformed penis, I concluded that these organs were of

this nature,--an excusable mistake, considering their almost ringed

structure, their somewhat constricted bases, the direction of their

curvature, and their position in the midst of the ova within the sack.

On careful examination, however, these appendages are seen not to be

truly ringed or articulated, but are covered with transverse lines of

scales, hirsute on their edges; these scales being less distinct, or

even quite absent on the smooth upper portion; they do not include

any muscles; they are imperforate at the apex, which is not furnished

with bristles (as seems always to be the case with the probosciformed

penis); and, lastly, they are lined by corium, but are not occupied

by any vessel, gland, or organ of any kind. The only function which

I can assign to these appendages, is that of aiding the retention

of the ova within the sack: for the ova, when first produced, are

aggregated round them; at this period I several times observed long,

somewhat curled, very thin fibres, not tapering like hairs, adhering

to both appendages, the nature of which fibres I cannot explain. In

very many cirripedes there seems a strong tendency to the production of

tapering, filamentary appendages, somewhat like the two (_i_, _k_) here

described,--namely, at the bottom of the sack in some Balaninæ, at the

bases of the anterior cirri in Lepas and in some other genera, and on

the dorsal surface of the prosoma in certain species of Pollicipes; in

this latter case some of these appendages were covered by scales; and

the prosoma whence they arose answers to the third segment of the body

in Cryptophialus, or that supporting the lower and larger appendage.

Appendages of this nature, in several cirripedes, serve for the

lodgment of the testes, but in some cases they are of no apparent use,

excepting, perhaps, in aiding respiration by the expansion of corium

thus exposed, and this partially may be their function here, for there

are no proper branchiæ.

_Cirri._--There are three pairs, together forming a nearly straight

brush, of considerable length, projecting in a line with the last

thoracic segment. Each cirrus is biramous. In a moderately large

specimen there were twenty segments in one of the longest rami. Each

segment (fig. 14, _a_) is strengthened by a dorsal or posterior shield

of thickened yellowish membrane, from the upper edge of which a single

smooth spine projects; the anterior surface is likewise strengthened

on the two edges by thickened membrane, and supports two pairs of long

spines, which are plumose, or rather hirsute, on both sides. In the

lower segments of both rami of the several cirri, the inner spine of

each pair is considerably shorter than the outer spine,--evidently in

relation to the little power of divergence of the two rami. All the

cirri resemble each other, excepting that the rami of the anterior

pair, are rather shorter than those of the other cirri, but the dorsal

spines on their segments are longer. In all ordinary cirripedes the two

rami are equally supported by the upper segment of the pedicel, which

latter is very short compared with the lower segment, and is separated

from it by a transverse articulation. Here (fig. 13) the exterior or

anterior ramus is articulated on the pedicel, almost like a branch, in

front of the other ramus, which seems more directly continuous with

the pedicel. The upper segment of the latter is separated from the

lower segment, both being of about the same size, by a very oblique

articulation. On the front surfaces of the pedicels there are two or

three pairs of spines.

_Abdomen._--The three cirri on one side are separated from their

opposite pairs by a prominent, longitudinal fold, formed of thickened

yellowish membrane, which, when foreshortened by being viewed dorsally,

looks like a style projecting immediately beneath the anus. The

transverse folds separating the three pairs, are exceedingly slight.

The inner basal edges of the pedicels of the cirri project slightly

inwards as apodemes, giving, I believe, attachment to some muscles. The

anus lies between the posterior pair of cirri, and deeply indents the

last thoracic segment. The transverse folds separating the three pairs

of cirri, little developed as they are, must, according to all analogy,

be considered as representing three segments of the body, and as we

have accounted for seven cephalic and seven thoracic segments, we must

conclude that these are three abdominal segments. We know, moreover,

that the abdomen in the pupæ of the Thoracica, with a single exception,

does actually consist of three segments.

_Movements of the Mouth, Thorax, and Cirri, &c._--Judging from the

fact of the lancet-shaped appendage of the labrum being more or less

exserted in dead specimens out of the shell-cavity, and from the

analogy of other cirripedes, I do not doubt that the whole mouth can be

considerably raised and depressed; we have seen, also, that the rostral

end of the toothed orifice of the sack can be pulled down, which would

aid in exposing the mouth and labrum. The well-articulated thorax,

by the aid of the muscles attached to every segment, can certainly

be doubled up and contracted, so that the cirri with their pedicels

(coloured purple like the exposed labrum) can be wholly protruded out

of the sack and shell-cavity. The three cirri no doubt can be separated

a little from each other, both transversely and longitudinally; and

according to analogy, the two rami of each cirrus can likewise be

separated: there are, also, muscles for moving the two segments of the

pedicel of each cirrus; and other muscles run up the many segments of

the rami. We have seen that the great lancet-formed appendage of the

labrum, laterally fringed with fine hairs, can be erected; and I do

not doubt that the prey when entangled by the expanded cirri, is borne

against this appendage, and is then, by the retraction of the thorax,

dragged down its smooth surface to the mouth, where it is seized by

the mandibles and maxillæ, which lie like a trap at the bottom of an

inclined and moveable plane.

_Alimentary Canal._--The œsophagus is long; it runs backwards from

the mouth and then downwards; at its lower end, where it enters

the stomach, the part, which in other cirripedes is expanded and

bell-shaped, is modified in a most singular and quite peculiar manner;

for the lower part of the œsophagus, after widening a little, becomes

converted into what appears at first like a square box, 8/1000ths

of an inch across. This box is really deeply folded (see diagram,

Pl. 24, fig. 11) into six longitudinal ridges and hollows: two of

these hollows, facing each other, are wider than the others, and when

the organ is dissected out of the body, it generally lies (fig. 10)

with one of these faces exactly over the other, the narrower lateral

folds being thus hidden, and the whole consequently appearing like

a simple square box with concave sides. But when a section is made,

or the lower open end is turned upwards, we see that the organ is

six-rayed and elongated, with the longer axis standing parallel to

the flattened sides of the animal's body. The edges of the folds are

formed of yellowish, thickened membrane, with a sinuous or beaded

outline, which serve to strengthen the organ. Internally, the two

broad concave sides are armed, in their upper inwardly prominent (fig.

12) part, each with a disc, 2/1000ths of an inch in diameter, crowded

with short, thick, brownish, inwardly projecting teeth. The two discs

stand exactly opposed to each other. The bases of the teeth, seen from

the outside (Pl. 24, fig. 10), seem like brown little circles, with

a smaller circle within. The disc obscurely appears to be formed by

the confluence of two smaller discs which lie, I believe, at a very

small angle to each other: beneath each of these half discs there is

a longitudinal band of very fine hairs, the two bands uniting into

one, lower down within the organ. The internal longitudinal edges,

also, of the four lateral smaller folds are likewise clothed with fine

hairs; hence we have six parallel longitudinal rows of very fine but

stiff hairs, or eight, if the united bands on the two broader faces

under the discs be counted each as two. These bands of hairs, and the

opposed discs, armed with very strong teeth, can be separated and

brought together with force, by the action of strong constrictor and

diverging muscles. Hence any prey carried down the œsophagus, before

entering the stomach, would have to pass, as it were through a mill,

and be subjected to a severe trituration by the discs of teeth, and

immediately beneath to a brushing by the six longitudinal bands of

hairs. This curious and unique structure answers, I believe, the same

purpose as the four convex, hardish, crenated buttons on the posterior

thoracic cirri in Alcippe, which are likewise unique in that genus. I

observed that in some specimens the teeth had been worn quite blunt,

but the teeth and hairs are periodically moulted and renewed, together

with the whole œsophagus.

The stomach is broadest at the upper end, and extends from a little

beneath the mouth down to the fifth segment of the body, where it

becomes narrow. It presented an irregularly contracted appearance, and

was covered by a pulpy hepatic layer. The rectum is of rather large

diameter; it extends from the middle of the fifth segment to the end

of the eighth segment of the body, or seventh of the thorax, where

the large anus is situated, lying between the posterior abdominal

cirri, and partly hollowed out in this seventh segment. The rectum,

as in all other cirripedes, is periodically moulted. The food is of

a bright green colour, as if of a confervoid nature; the triturating

and brushing action of the œsophagus seems to roll this matter into

pellets, which apparently retain this form until finally expelled as

excrement: certainly the excrement is in pellets, and I have several

times seen pellets within the stomach.

_Organs of Generation._--The specimens as yet described are exclusively

female, there being certainly no testes or vesiculæ seminales. As in

every specimen collected (early in January) there were within the sack

either nearly mature eggs, or young larvæ, it was the worst period for

seeing the ovarian cæca, and I have failed to discover them in the

specimens now long kept in spirits of wine; but I cannot doubt they

would be found, between the inner and outer tunics of the carapace or

general covering, near the disc. I have stated in my original notes,

made when the specimens were alive, that the ova are at first perfectly

detached; but some appearances make me believe that I overlooked (as

might easily happen) the often _excessively_ fine membrane which in

other cirripedes unites the ova together, and so forms the ovigerous

lamellæ. The ova are much less numerous than in other genera, varying

from only nineteen to about sixty. In the same individual all the eggs

were always in the same state of development.

_Metamorphoses._--The true ova, in their earliest condition, when in

the sack, are ovate (Pl. 24, fig. 15), orange-coloured, quite smooth,

and barely 10/1000th of an inch in their longer axes. They soon become

broader at one end than at the other; and by degrees the narrow

posterior pointed end becomes developed into a slightly club-shaped,

almost transparent (fig. 16) horn, and the broader anterior end, into

two rather longer horns. The length of the oval part, not measuring the

horns, is nearly the same as in the primary true egg condition. There

is as yet no trace of internal organs, the whole contents consisting

of pulpy granular matter. How far the above changes are effected by

moulting, either of the whole or of part of the integuments of the

egg-like body, I cannot say; but the pulpy matter within the ovum, even

in its earliest stage, was included within an inner envelope or case.

In the next distinct stage (there being, however, slighter intermediate

changes) the posterior horn has shrunk, and become converted into a

bluntly-pointed conical termination for the whole body (fig. 17),

whereas the two anterior horns have approached each other on the

future ventral surface, and have increased considerably in length and

thickness, and contain within them the prehensile antennæ, which can be

externally seen, and which I dissected out of these horn-like cases.

The oval part of the egg-like larva (for I hardly know what to call it)

is now very slightly shrunk, being hardly more than 9/1000ths of an

inch in length. At this stage, these bodies adhere by the tips of their

anterior horns, containing the antennæ in process of formation, to the

inner tunic of the sack, and likewise in little groups one to another:

as the included prehensile antennæ ultimately become attached by cement

(proceeding, no doubt, as usual, from a modified portion of the ovarian

tubes), it seems probable that some cement may at this early period be

excreted, but I could not make out the exact means of attachment. The

egg-like larvæ are, also, aggregated round the tapering curled dorsal

appendages of the second and third segments of the body, and it is

possible that at this, or at an earlier period, these appendages may

act like the ovigerous fræna in the Lepadidæ, and serve to retain the

egg-like larvæ within the sack.

We come now to the last larval, or pupal condition, before the final

metamorphosis into the mature animal; the changes above described have

been, at least to a great degree, if not absolutely gradual; but the

pupa suddenly appears perfectly developed, from the moulting of the

last-described horned, egg-like larva. It is now a free animal crawling

about the sack of its female parent. It has increased a little in

length, as compared with the oval part of the egg-like larva in its

second stage, namely, from a little above 9/1000ths to 16/1000ths of an

inch: from the position of the prehensile antennæ in the two states,

I have no doubt that this increase of size is entirely due to the

anterior part of the pupa being doubled up whilst within the egg-like

larval envelope. The pupa in shape (fig. 18) somewhat resembles a

coffin, and is far less laterally compressed than other pupæ, and

hence can easily be placed either on its dorsal or ventral surface.

The prehensile antennæ are of large size: when the animal was alive,

they were concealed under and partially included within, the front

part of the carapace or shell, which in this condition was not so much

truncated as in the drawing given (fig. 18) of a specimen lying on its

back, with its antennæ protruded. Some specimens formerly examined for

me by Dr. Hooker, had their antennæ and whole ventral surface forced

outwards, apparently from the endosmose of the spirits of wine. The

whole dorsal surface, and the overlapping sides of the carapace are

elegantly punctured, and are formed of a rather brittle substance, here

and there supporting, especially at the front end, some fine and rather

long bristles,--which latter I have not seen on the pupæ of other

cirripedes. The ventral surface is very narrow towards the posterior

end of the animal; it is formed of thin, structureless membrane. On

this surface, close to the posterior end, there is a minute orifice,

through which three pairs of bristles are protruded, attached to (as

I believe) the rudimentary abdomen; the bristles apparently cannot be

withdrawn.

The antennæ, (fig. 18) as stated, are of large size compared to the

whole animal: they resemble, in all essential respects, the same organ

in other cirripedes. The ultimate segment is unusually thick;[152] it

is terminated by five bristles, one of which is longer than the others,

and stands rather separated from them. The disc-segment is large,

nearly circular, with the broad edges transparent and membranous;

on its posterior edge there is a single small spine. The second or

main segment, counting from the base, has a single spine on its upper

margin, close beneath the spine on the disc; it is articulated to

the disc-segment, a little way from the disc itself,--which is a

peculiarity I have not elsewhere noticed. The basal segment is thick

and not so short as usual. These organs are furnished with powerful

muscles. They are generally protruded alternately; and by the adhesion

of the sucker-like disc, the animal drags itself along. The sucker-disc

has great play, and when observing specimens alive, I compared its

action to that of a wrist-joint. The antennæ, when retracted within

the carapace, lie parallel to each other.

[152] As I have given, in my former volume on the Lepadidæ, p.

286, so many measurements of the antennæ, I may here add those of

Cryptophialus,--the length from the end of the disc to the end

of the second segment, (formerly called by me, erroneously, the

basal,) is 26/6000ths of an inch; the greatest width of the second

segment, 9/6000ths; the length of the little ultimate segment,

3/6000ths, and its width under 3/20000ths of an inch.

Posteriorly to the antenna, I distinctly saw the apodemes to which the

eyes are attached: I was not able to distinguish any middle fork to the

apodeme, which consequently does not resemble a UU, but U. The eyes are

dark purple, and, as usual, compound: in one specimen I counted twelve

ocelli within the common spherical envelope.

I could not distinguish any thorax, and certainly there is no mouth;

nor, from analogy, could the latter be expected, excepting as forming

part of the young cirripede: there are no natatory legs, which the

pupæ in all other cirripedes possess. Of the three postero-ventral

pairs of bristles, the most posterior or dorsal pair, differs from the

other two pairs in being considerably smaller, and in being mounted

on elongated pedicels: the two anterior pairs of bristles are strong:

the three pairs are articulated, one behind the other, on a small

body, apparently enclosed in a minute sack, and certainly attached all

round by membrane to the internal edges of the orifice, through which

the bristles are protruded. These bristles, when the pupa was alive,

were often moved, and served apparently to steady the body during the

alternate protraction and retraction of the prehensile antennæ. From

the fact of the pupa of other cirripedes having an abdomen, formed of

three segments, placed exactly in the same position as the minute body

here supporting the three pairs of spines, I believe this body to be

the abdomen. In other cirripedes only the posterior segment of the

abdomen bears spines, which are supported on little limbs or pedicels,

namely, the caudal appendages, the other segments being naked. But as

the mature Cryptophialus, unlike other cirripedes, has abdominal cirri,

the presence of spines on the corresponding abdominal segments in the

pupa, is explained and rendered probable: there can, I think, be little

doubt that the small terminal pair of spines, supported on elongated

pedicels or limbs, answers to the caudal appendages found in many

cirripedes.

The whole course of the metamorphosis is very peculiar. The gradual

changes in the egg-like larvæ (for I suppose they must be called larvæ)

from a simple oval egg, to pointed oval, to oval with three horns, and

lastly to oval with the two anterior horns larger, and the posterior

horn reduced to a mere point, seems to me very curious; and offers, as

far as I know, a unique case. It is interesting to reflect how perfect

a series, in the development of an animal, we have, in different

members of the Articulata,--from an ordinary egg, in which all the

changes go on unperceived, and whence a perfect animal is matured,--to

an egg-like larva which undergoes the changes just described, and which

turns into a pupa that does not eat or increase in size,--to a larva

which eats and increases in size, but undergoes only one great change,

as in most insects,--to a larva undergoing several great changes, as in

the case of ordinary cirripedes, before its final metamorphosis into

the mature animal. The first larval condition of other cirripedes, in

which there is a single eye, three pairs of thoracic limbs, and a much

elongated pointed body, covered by a prolongation of the carapace,

is here not fully developed or matured; but this stage is, I think,

clearly and very curiously indicated by the posterior horn of the

egg-like larva, which we may suppose represents the posterior pointed

end of the body, for it disappears in the succeeding stage, just as it

does in the second larval condition of other cirripedes. In the first

stage of ordinary cirripedial larvæ, the anterior horns are always

present, serving, as in the case of these egg-like bodies, to enclose

and protect the antennæ during their formation. The second egg-like

stage answers to the second larval condition of ordinary cirripedes,

as described (and figured, Pl. 30, fig. 1) in the introduction to the

Balanidæ. The third or pupal state is fully developed in all cases.

Finally, the pupa of Cryptophialus is peculiar in its punctured, hairy

surface, and in its shape, which, in being so much more depressed than

usual, retains an earlier larval condition; but its chief and highly

remarkable character consists in the entire absence of natatory legs;

and, in consequence, instead of there being a large sack within the

carapace, with an elongated orifice on the ventral surface, there is

only a quite minute orifice at the extreme posterior end of the animal,

through which the bristles, borne apparently on all three segments of

the minute abdomen, are protruded.

The pupæ of the male and female are exactly alike in all their general

characters, and probably in every point of detail; but my later and

more minute observations were made only on pupæ, which, from their

place of attachment, would certainly have turned into males. As these

pupæ, without any further metamorphosis, were developed into males, we

may, I think, safely infer that such is the case with the females: and,

consequently, that the whole course of the metamorphosis has been, in

this cirripede, seen and described. During this whole course, no food

could possibly have been obtained, for the pupa is destitute of a mouth

or organs of prehension, and the stock of cellular matter, enclosed

within the ovum, has been sufficient for all the above changes, and for

the final metamorphosis. We shall, moreover, immediately see, in the

case of the male, that the stock of cellular matter has also sufficed

for the development of testes, spermatozoa, and a wonderfully elongated

probosciformed penis.

MALE. Pl. 24, fig. 19.

By throwing pieces of the perforated shell of a Concholepas into

acid, I examined several scores of specimens of the Cryptophialus,

and on all, with the exception of a few young individuals, males were

attached. They were attached by cement, proceeding in the usual manner

from the prehensile antennæ, outside, to the edges of the upper half

of the disc formed of the thicker not-moulted membrane, by which the

female adheres in her chamber: hence the males are included in the

upper part of the same cavity with the female, into which they must

have crawled as pupæ. I found from one or two up, in one case, to seven

males, attached to the same female; four or five being the most usual

number. In the early part of January, when all my specimens were taken,

many of the males had not shed their pupal integuments, and of those

that had, the majority were immature, a few only having spermatozoa:

all the females had within their sacks, either ova including almost

perfect pupæ, or fully developed pupæ: we may, consequently, conclude

that these young males were maturing in order to impregnate the next

set of eggs.

The male, immediately after its metamorphosis from its pupal condition,

which has been fully described, is almost globular, but slightly

bilobed, and is formed of strong, structureless, transparent membrane,

including a mass of cellular matter, apparently without any included

organs: it is attached by about the middle, between the anterior and

posterior lobes, by the not-moulted prehensile antennæ. When the male

is mature, its greatest length, measured from the posterior end, where

the orifice is seated, to the anterior and blunter end, is about

13/1000 of an inch, and therefore rather less than the pupa, which

was 16/1000ths in length. Relatively to a full grown female, the male

slightly exceeds half the diameter of the toothed orifice leading into

her sack, see (_z_) fig. 1, Pl. 23. In the mature condition, (fig. 19),

one lobe, namely, the upper or posterior, has become more pointed, and

is terminated by a minute orifice, 8/6000ths of an inch in diameter.

This orifice is formed by a rim of thickened brownish membrane, which,

on what was the ventral surface, has a few very minute, but strong,

sometimes bifid spines;--in this one character, the male resembling

the female. The other and lower (homologically anterior) end or lobe

is broader, and contains a mass of cellular matter, which, from its

close resemblance in appearance and position to similar matter within

the male Alcippe, I have no doubt forms the contents of the testis.

In one single specimen, I succeeded in isolating a vesicula seminalis

of small size, containing perfectly distinct spermatozoa. Across the

middle, between the two lobes, close under the outer integument,

there is a broad layer of rather strong transverse muscular fasciæ.

I did not observe any eye, the presence of which I should have

expected from analogy. Internally there is no mouth, thorax, cirri,

or other organs, excepting the testis and vesicula seminalis just

mentioned, and an immensely elongated probosciformed penis, coiled up

and filling the rest of the inside of the sack down to the testis,

which latter occupies the whole anterior, and generally lower end

of the animal. This penis is plainly articulated, and includes fine

transversely-striated muscles: no doubt it can be protruded through

the minute orifice, and voluntarily moved about. Out of a male,

12/1000ths of an inch in length, I dissected a penis, which, when not

stretched, measured 50/1000ths of an inch in length; when a portion

was pulled between two needles, it could be stretched to apparently

three times its former length, and I should think that this organ

could be extended by the animal to, perhaps, even the 100/1000ths of

an inch,--that is, to between eight and nine times its own entire

length! The use of this enormously elongated penis obviously is,

that the spermatozoa of these males, which are so extremely small in

size, compared to the female, should all be conveyed within the sack,

and none be lost. It should be borne in mind, that the whole male,

including every part, is scarcely larger than a single ovum, of which

sometimes sixty have to be impregnated by only two or three males. In

a full-grown female, the distance from one of the attached males to

the middle of the orifice leading into the sack, is about the 5/100ths

of an inch, equal to the length of the coiled up, not-extended penis:

the further distance from the orifice of the sack to an ovum lying at

the bottom of the sack, would be almost 10/100ths of an inch, so that

the spermatozoa have to pass a distance of 15/100ths of an inch from

the testis of the male to the lower ova. I believe two thirds of this

distance would be passed safely along the probosciformed penis.

The resemblance between the male of Cryptophialus and of Alcippe is

truly surprising; and is the more wonderful, considering the great

dissimilarity of their pupæ. Hardly any characters can be pointed

out in which these males differ, excepting such as might have been

thought of only specific value, namely the relative proportions of the

different parts, and mere external shape. The peduncle growing a little

after the metamorphosis, in the male of Alcippe, and the prolongation

of its capitulum with the included oblique ligamentous fibres, are the

greatest differences. Having fully remarked, under Alcippe, on the

wonderfully rudimentary condition of these males, destitute as they are

of so many parts and organs, I will here say nothing further on these

singular creatures, destined to discharge their spermatozoa, die, and

be succeeded by a fresh set of short-lived male successors.

Order III.--APODA.

_Cirripedia, with the carapace reduced to two separate threads, serving

for attachment: body consisting of one cephalic, seven thoracic, and

three abdominal segments, all destitute of cirri. Mouth suctorial, with

the mandibles and maxillæ placed back to back, enclosed in a hood,

formed by the union of the labrum and palpi. Metamorphoses unknown._

The characters above given fully justify, I think, the formation of

this order; though it contains only one species, the _Proteolepas

bivincta_. The mere external appearance (Pl. 25, fig. 7), so

wonderfully different from that of every other cirripede, would by

itself prompt to this same conclusion. At first sight the Proteolepas,

if of fresh-water origin, might even have been mistaken for the larva

of some insect, fastened by two threads to its prey. The entire

absence of the three anterior segments of the head and therefore of

the carapace, or, speaking strictly, the mere rudiment of these parts,

forming an envelope to the two cement-ducts,--the absence of a stomach,

rectum, and anus,--the entire absence of thoracic and abdominal

appendages or cirri,--the absence of a probosciformed penis,--are all

negative characters, which might ensue from degradation, so common

with parasites; and which might, therefore, have been esteemed of not

high classificatory value. But the suctorial mouth, with the palpi and

labrum united into a hood, and with the mandibles and maxillæ reversed

or turned back to back, so as to be utterly incapable of prehension,

is a type of structure not hitherto met with, I believe, in any other

animal, and cannot be explained away by degradation. The formation of

the ova within the segments of the body, a peculiarity confined to

this one cirripede, evidently results from the non-development of the

anterior part of the head, within which the ova are usually formed;

but the compound structure of the vesicula seminalis is a peculiarity

which cannot be thus explained. Proteolepas has no particular affinity

to any other cirripede; it resembles, indeed, Cryptophialus in one

important point, but only in one point, namely, in the number of the

segments of its body. It is really beautiful to see how the homologies

of the archetype cirripede, as deduced from the metamorphoses of

other cirripedes, are plainly illustrated during the maturity of this

degraded creature, and are demonstrated to be identical with those of

the archetype Crustacean. I was at first inclined to rank Proteolepas

in one division, and all other cirripedes in another division of

equal value; but as it may be inferred from the characters of the

prehensile antennæ, that the pupa did not differ much, if at all in any

important character, from the pupæ of other cirripedes, I have thought

the three orders, which I have instituted, would be the most natural

arrangement. As any one looking at the drawing given of Proteolepas,

might very naturally feel inclined to protest against its being ranked

as a cirripede, I must reurge the importance of the pupal antennæ

being constituted on the common type, for from their structure, by the

law of correlation, that of the whole pupa may be inferred; and even

still more I must insist on the importance of the one great character

of the antennæ being cemented to the surface of attachment by matter

proceeding, as we shall see, in a modified state, from the great

ovarian sack. The structure, also, of the mouth (to a certain extent),

the segmentation of the body, though in appearance so peculiar, the

hermaphrodite condition, the single penis, the absence of oviducts, all

accord with, and taken together demonstrate, its cirripedial nature.

PROTEOLEPAS BIVINCTA. Pl. 24, 25, figs. 1-7.

_Hab._--Parasitic within the sack of the _Alepas cornuta_, from St.

Vincent's, West Indies, Brit. Mus.

_General Appearance._[153]--The entire animal, as already remarked,

curiously resembles, at the first glance, the larva of some insect.

It is rounded, but somewhat compressed, and tapers gently towards the

posterior end. It lies curved in an arc, the ventral surface being

concave, and the dorsal convex, but a little flattened dorsally at the

anterior and blunter end. Its length, if straightened, would rather

exceed one fifth of an inch. The body consists of eleven segments,

which, excepting the three terminal, are conspicuously plain. The

first segment is surmounted by a rather small mouth, which any one

would, assuredly, at first consider as the entire head, though he

would in vain search here for eyes, antennæ, or other parts of the

three anterior cephalic segments. On the dorsal surface, low down on

the second segment of the body, two, quite flexible, thin, but strong,

flattened threads arise, which terminate in a pair of prehensile

antennæ, having the usual cirripedial structure. From the penultimate

or disc segment of these antennæ, cement has been excreted, by which

the antennæ are firmly cemented low down to the rostral end of the sack

of the cirripede, the _Alepas cornuta_, on which it is parasitic: hence

Proteolepas lies with its back downwards, and with its ventral concave

surface fitting the convex body of the Alepas: its mouth lies under

the middle of the soft prosoma of the latter cirripede, which I cannot

doubt that it lacerates and sucks.

[153] I may be permitted to premise, that though I procured only a

single specimen, yet perceiving its very singular nature, I took

such care and length of time in the dissection, and repeated every

observation so many times that I think reliance may be placed

on the description here given. Fortunately I had acquired, from

dissecting many much smaller specimens of various cirripedes, all

the advantage which full experience could give me, when I commenced

on Proteolepas.

_Mouth._--The mouth is suctorial, and is constructed on a different

plan from that in any other cirripede, or, indeed, in any other,

as far as I know, articulated animal. It is narrower, in both a

longitudinal and transverse plane, than the first segment of the body,

and is distinctly separated from it. The lower part on the ventral

side, is protuberant and rounded. The summit is square, and is formed

by the crest of the labrum, with two large palpi (_d_, fig. 3), having

nearly the usual form amongst the Balaninæ, and pointing towards each

other, but differently from in any other Cirripede, they are united

for their whole length to the labrum, and by their extremities to

each other. These parts together thus form an arch or hood, within

which stand the other gnathites. The palpi are roughened by groups

of very minute spines. At their bases they can be obscurely seen to

be separated from the rest of the mouth by an oblique joining or

articulation. The back of the mouth is formed entirely of the labrum,

which becomes narrow towards its base: it is, from top to bottom,

20/1000ths of an inch in height. Within the hood formed by the palpi

and labrum, a pair (_c_, fig. 3), of very singular, compounded,

mandibular organs project freely, straight up, with their convex outer

edges placed parallel and close together, and their teeth pointing

directly from each other, so that they stand in a reversed position

compared with the jaws of all other cirripedes, and are absolutely

incapable of prehension.

This compounded organ is singularly small compared with the palpi and

labrum: it is narrow, being about 5/3000ths of an inch in width, but

is produced upwards, so that a considerable length projects freely,

and the rounded, properly external, margin can be traced down for a

length of about 20/3000ths of an inch. In a lateral view of the mouth,

the extreme tip of the mandibular organ could sometimes be seen just

projecting out of the hood. The mandibular organ, when separated and

carefully examined, presents the appearance, represented from a camera

drawing, in (Pl. 24, fig. 2): we here see three groups of teeth; of

these the lower set (_c_) consists of blunter teeth, placed more

transversely, and easily separated from the others, and altogether

clearly appears like a distinct organ. I do not feel nearly so sure

regarding the other two sets; my first impression was strongly that

they were distinct organs, closely united laterally together,--one

(_a_) probably representing the mandibles, and formed into a single

large tooth; the other (_b_) formed of three teeth, and probably

representing the outer maxillæ; the first-mentioned set of teeth, which

seemed to me to arise from between the other two sets, being the inner

maxillæ. If this view (and it must be remembered how excessively minute

the parts are) be not, as I now suspect, correct, we must suppose

that the outer maxillæ are aborted, and we have seen some tendency

towards this in other cirripedes; the compounded organ being formed

only of the mandibles (having on this view four teeth) and the inner

maxillæ. As far as the mandibles are concerned, their existence, I may

remark, is plainly shown by the presence of the palpi, which in all

cases belong to and form part of the mandibles. The ventral surface

of the mouth, immediately beneath the free portion of the compounded

mandibular organ, consists of a triangular projection, but I could

see no appearances to make me suppose that this part represented

the outer maxillæ. The compound organ--in general shape, and in the

oblique manner in which the front part is cut off and terminates in

ligamentous apodemes, to which muscles are attached,--presents an

unmistakable likeness to a mandible. It is hollow within, and muscles

appear to extend some way up, perhaps to the transversely toothed

portion, which represents, as I believe, the inner maxillæ: these two

groups of teeth, anyhow, seemed to have some power of sliding over each

other, and altered their positions during the course of dissection. On

each side of the mouth, there is a muscle attached by its lower end

to the basal edge of the labrum, and two others, one above the other,

attached by their lower ends to about the middle of the labrum; these

muscles, which are distinctly striated or voluntary, I infer, from

analogy, run up to the ligamentous apodemes of the compound mandibles.

There appeared to be other more delicate muscles attached to the basal

articulation of the mouth on the ventral face, and these, I presume,

would run to the supposed inner maxillæ.

The mouth in forming a prominence separated by a distinct articulation

from the body, and in the union of the palpi and labrum (though here

carried to excess), is constructed so far on the cirripedial type; but

how are we to account for the extraordinary reversed position of the

united mandibles and maxillæ, with their backs almost touching each

other, and their toothed edges twisted round so as to face outwards

in a manner unexampled, I believe, in any other articulate animal? It

might, perhaps, be at first suspected, that the compounded mandible had

not really been twisted round, but that the teeth had been abnormally

developed on the outer convex margin: this view, however, certainly

cannot be admitted, for the properly outer convex margin can be traced

running far down the mouth, in a manner utterly inexplicable, if this

were really the inner side; and equally inexplicable on this view would

be the position of the ligamentous apodemes. Hence I cannot doubt

that this compounded mandibular organ has really rotated on its axis;

and if the course of development could be followed, I suspect that

the twisting would be seen to be effected as follows: we know in all

cirripedes that the outer and inner maxillæ, and to a certain extent

the mandibles, instead of facing each other, are directed towards the

labrum; they therefore have already been twisted round a quarter of a

circle, as may be seen in the diagram (Pl. 24, fig. 4), copied from the

mouth of Ibla. Now let us drive inwards the front of the mouth, along

a narrow medial line; these organs would then (fig. 5) be compelled to

turn round a quarter of a circle more, and so face directly outwards.

In this process, the integument between the lower and outer part of

the mandible and the base of the palpus, which normally are in close

contact, would have to be greatly stretched. By a movement of this

order, the mandibles would come to stand posteriorly or exteriorly to

the other gnathites; and as far as I could make out (previously to my

having any theory) the large single toothed portion of the compound

organ which most resembles a mandible, did really stand outside the

other toothed portion.

With respect to the action of this singularly constructed mouth; if

its ventral and oblique surface were applied to any yielding object,

as the adjoining soft prosoma of the Alepas, the compound mandibles

would be worked within an absolutely closed chamber. The action of

these mandibles would be to make a transverse slit, and subsequently

to serve as a grapnel to keep the mouth closely adpressed to its

prey: the other teeth might act in keeping the wound open. When the

mouth was thus closely adpressed over a wound, the great power of

shortening the whole body which the animal possesses (the œsophagus

being closed), would, by the subsequent action of the elasticity of the

outer membrane, almost certainly create suction, and thus cause the

nutritious juices of the Alepas to flow into the body of the parasite.

Hence I have called the mouth suctorial.

_Body._--This, as already stated, consists of eleven segments, of

which the three posterior (abdominal) smaller segments can hardly be

distinguished, without dissection, as separate from each other. The

body is mainly occupied by a vast ovarian sack (_e_, _e_, fig. 7),

filled by innumerable ova: and the three posterior segments by small

testes and their vesiculæ seminales (_i_): but I shall return to

the internal anatomy. The outer membrane, lined by delicate corium,

is thin, transparent, elastic, and covered by groups of excessively

minute blunt little points. The segments can be plainly distinguished

by their outlines, especially on the ventral surface; but they are

rendered unmistakably distinct by the attachment of the muscles; they

can also be perceived when the external membrane is perfectly cleaned,

by yellowish lines. The muscular system is highly symmetrical and

simple: along all eleven segments, there is a narrow, medial, ventral

and dorsal clear space; on both sides of which space there is a band

of longitudinal muscles, which, though encroaching on the two sides,

and rather largely on the dorso-lateral sides, may be called the

ventral and dorsal muscles. These muscles are striæ-less, which is

the case with the homologous posterior thoracic muscles in some other

cirripedes: on the dorsal surface (lower surface in fig. 7) they are

more spread out, and consist, on each side of the medial line, of four

ribbons: this seems to be the case on the ventral side, but the ribbons

are here much more confluent: in the seventh and eighth segments, the

ribbons become broader; but in the ninth, tenth, and eleventh, or

three posterior segments, they become much narrower, and some of the

fasciæ disappear, so that these muscles can hardly be seen from the

outside. Each separate ribbon expands a little at its two ends, which

are attached to the articulations separating the successive segments:

I carefully observed that they did not pass over at either end to the

adjoining segments: hence their action must be either simply to shorten

and arch each segment separately; or when acting together, to shorten

the whole body, or perhaps the ventral or dorsal surface by itself.

In the first segment, and in the three posterior segments, these

longitudinal muscles alone occur; but on the seven segments, from the

second to the eighth inclusive, there are other oblique latero-ventral

muscles. These muscles lie within the longitudinal muscles, and

adhere pretty firmly to the coat (_e_, _e_, fig. 7) of the great

ovarian sack. At their ventral extremities they are attached, near the

anterior margin of each segment, beneath the point of attachment of

the longitudinal fasciæ, and thence they run posteriorly in an oblique

line to the anterior margin of the next succeeding segment, where

they are attached: so that these muscles run obliquely from segment

to segment. The first of these oblique muscles, lying chiefly within

the second segment of the body, is thinner and longer than the others:

those within the third and fourth segments are short: those within the

fifth and succeeding segments extend, at their dorsal (or lower in

fig. 7) extremities, as far as the outer dorsal longitudinal fasciæ:

those within the seventh segment are broad and short, and cross the

longitudinal muscles at only a small angle. In the eighth segment,

there is an oblique lateral muscle, like that in the seventh segment,

running from the ventral surface towards the dorsal surface; but there

is in addition a second oblique lateral muscle, rising from the dorsal

surface, and running towards the ventral surface. This muscle does

not occur in the other segments, but in the fourth segment, at the

dorsal end of the oblique latero-ventral muscle, there may be seen

a small branch of fibres, at right angles, which seems to represent

a muscle homologous with that just mentioned in the eighth segment:

obscure traces, moreover, of similar fibres, can be detected in some

of the other segments: had these oblique latero-dorsal muscles been as

fully developed in the seven anterior segments of the body, as on the

eighth segment, the whole muscular system would have been perfectly

symmetrical. The oblique latero-ventral muscle in the sixth segment is

distinctly striated transversely; but this is not the case with most

of the other muscles, if with any of them; I cannot account for this

difference. The muscles of the gnathites are the only other voluntary

muscles in the animal's body.

_Homologies of the Body._--It will hereafter be, I think, clearly

shown, that when the shell and integuments of the pupa of Proteolepas

are shed, no carapace or general covering for the body is formed; the

three anterior segments of the head, the backward prolongation of

which (as has been elsewhere explained) certainly forms the carapace

of ordinary cirripedes, being here almost absolutely aborted. In every

cirripede the mouth is formed of three pairs of gnathites, which, no

one will doubt, rise from the fourth, fifth, and sixth segments of

the head: here in Proteolepas, the mouth, even on the view of the

mandibular organ on each side being compounded of only two gnathites,

sufficiently resembles the ordinary cirripedial type to make it very

probable, that if examined in the earliest stage of its development,

three pairs of gnathites would be discovered. In accordance with

this conclusion, the segment succeeding the mouth (_i. e._, the

first segment of the body in fig. 7) homologically is the seventh,

or last cephalic segment. The succeeding seven segments, of course,

are the seven thoracic segments, and the three posterior segments

are abdominal; the latter are not developed in ordinary cirripedes

when mature, but are present during their pupal condition. Now this

conclusion, which is, in fact, deduced from what we know of the front

part of the head in other cirripedes, both larval and mature, appears

to me most satisfactorily confirmed by the differences in the muscular

system of the segments in Proteolepas. In no other way, I believe,

can it be explained, why the last cephalic segment and the three

abdominal segments should differ from the seven thoracic segments,

in the entire absence of the oblique lateral muscles. The abdominal

segments, moreover, differ a little in shape, in the indistinctness

of their articulation, in the thinness of the longitudinal muscles,

and even in their contents. With respect to the two threads enclosing

the cement-ducts, which spring from the second segment of the body

(or first of the thorax), and which terminate within the prehensile

antennæ of the pupa, we shall hereafter see that their apparently most

anomalous position, and even the flattened shape of the dorsal surface

of the two anterior segments of the body, all accord perfectly with the

homologies just given.

_Alimentary Canal._--The œsophagus is thin, and for a cirripede short,

for it extends only half-way down the first segment (_i. e._ last

cephalic) of the body; the lower end, which is slightly dilated, nearly

touches the anterior end of the great ovarian sack. At its upper end,

it is surrounded by delicate, striæ-less constrictor muscles; and there

are others radiating outwards, evidently serving to open it: the lower

part of the œsophagus, differently from other cirripedes, is destitute

of muscles, and is only coated by a thin layer of corium, which would

serve to produce a new œsophagus at each exuviation. Strange as

the fact may be, I am prepared to assert that there is no stomach,

rectum, or anus. As I was able to trace so distinctly the œsophagus,

and likewise the generally far smaller orifice and ducts of the male

generative organs, I consider it quite impossible that I could have

missed the stomach. The rectum and anus are absent in Alcippe: and the

absence of a stomach is here in some degree the less surprising, as the

structure of the mouth shows that Proteolepas must live on the already

elaborated fluids of the Alepas, to which, being a cirripede, it is

allied. It is of some importance to observe, that the œsophagus is

fitted with muscles simply for shutting and opening it, the wave-like

swallowing action of which other cirripedes are capable, being,

apparently, here impossible; but the contraction of the body and its

subsequent expansion, the œsophagus being opened, would allow the blood

of its prey to flow inwards.

The nervous system must be much atrophied, for I could not detect

it, and the small size of the animal is not sufficient to account

for this: I wish I could have seen this system, for then I should

almost certainly have beheld an articulate animal without a trace of a

supra-œsophageal ganglion. There is no eye, but such could hardly be

expected, as the anterior cephalic segments are aborted. There are

no branchiæ. I may state that within the abdomen, along the dorsal

surface, there was either a lacuna or a delicate vessel, apparently of

a circulatory nature, of considerable diameter, which, near the extreme

posterior end of the body, gave out branches.

_Female Reproductive Organs._--The eight anterior segments of the body,

with the exception of a small space at the two ends, are occupied by

an immense (_e_, _e_), opaque, ovarian sack. The tissue forming it

is delicate, and presents a peculiar cellular aspect: it is slightly

attached to the corium on the ventral surface of the body, and to the

oblique latero-ventral muscles. Internally, at the anterior end, it is

thickly coated by cellular matter, the cells varying from 4/6000ths to

less than 1/6000th of an inch in diameter, becoming in parts confluent,

and the whole forming a dark orange-coloured mass. In the more central

parts of the sack this cellular matter became aggregated into little

pellets, which, in proceeding towards the posterior end of the sack,

gradually increased in size, from about (4 to 6)/1000ths of an inch in

diameter, and at last appeared as almost mature and perfect ova of a

broadly oval figure. Their size, as we see, is small, and their number

almost infinite. I carefully examined all round this ovarian sack, and

could detect no oviducts; nor from analogy could they be expected: I

have no doubt that the ova burst forth by the rupture, probably, of the

posterior end of the sack and of the overlying corium; and that they

accumulate beneath the external membrane of the body, until this is

moulted, the rupture beneath being in the meantime healed, when they

are freed, or perhaps temporarily protected in the old moulted envelope

of the body.

On each side, within the first two segments of the body, and projecting

a little before the great ovarian sack (_e_), two gut-formed organs

(_f_) may be seen, even from the outside, owing to their opacity and

dark colour. They lie near the external surface; the first pair of

latero-ventral oblique muscles passing between them and the ovarian

sack. They are formed of a branching, grape-like mass of opaque,

orange-coloured cells. They are intimately united, at their posterior

extremities, to the ovarian sack, and I believe open into it; but I

cannot say that I demonstrated this. From their absolute identity in

structure, and similarity in position, namely, on each side of the

lower end of the œsophagus, no doubt is left on my mind that these

bodies answer to the true ovaria, which are situated within the body of

other cirripedes; and that the ovarian sack answers to the inosculating

and branching ovarian tubes and cæca, which fill the peduncle, or cover

the basis in other cirripedes, but here, from the absence of these

parts, necessarily occupying the body.

_Male Organs._--The whole surface of the ovarian sack, the space before

it, even to within the lower parts of the mouth, the posterior half of

the last thoracic segment, and especially the whole three abdominal

segments, are completely netted by branching delicate vessels or ducts

terminating in spherical glands about 1/2000th of an inch in diameter.

These little glands include a brownish pulpy centre, and sufficiently

resemble the testes of other cirripedes in appearance, position, and

connecting ducts, to make me believe that such is their nature. I

may remark that in the more central parts of the abdomen the glands

and ducts seemed to be in process of formation by the confluence of

cellular matter, and in some other cirripedes I have suspected that

the testes are periodically renewed, or at least redeveloped from

an undistinguishable condition. Within the posterior half of the

abdomen, some of the ducts become thicker and unite, others joining in

laterally, so as together to make a dark chord, 7/2000ths of an inch

in diameter. Until dissecting this chord, I thought it was a single

vesicula seminalis, but it separated into several rather thick ducts

or vesiculæ. I was not able to remove from within them the contained

matter, but it appeared very finely and longitudinally flocculent, like

spermatozoa not quite matured. In accordance with the immature state of

the contents of the ovarian sack, in all probability these ducts would

hereafter have become greatly enlarged, and have formed a compound

vesicula seminalis of considerable size. The dark chord, formed

by their union, contracts as it enters the rudimentary penis, and

terminates in a very minute orifice on its apex. The penis consists of

a papilla, only 3/4000ths of an inch in length, situated on the extreme

point of the abdomen, but rather towards the ventral surface.

_Metamorphosis._--In accordance with the general law of the correlation

of parts, it may be inferred, from the description and measurements

of the pupal antennæ immediately to be given, that this abnormal

creature was developed within a pupa of the same general structure,

and of about the size, as the pupæ whence Scalpellum, Alcippe, and

many other cirripedes are developed. As the ova are of remarkably

small size, indeed I have seen no others quite so small, it is certain

that the larvæ, as in the case with all other cirripedes, excepting

Cryptophialus, must undergo several metamorphoses, and increase much in

size, before attaining their pupal condition.

_Attachment._--The animal is attached, as already stated, to the

sack of the Alepas by two threads, rising close together from the

medio-dorsal line, near the posterior end of the second segment of

the body. These threads are attached likewise close together at their

further ends, by the antennæ, into which they enter. They are flattened

and strong, yet quite flexible, with a somewhat sinuous surface: they

were, in this specimen, 42/1000ths of an inch in length, and a little

above 3/1000ths in diameter: where joined to the thoracic segment they

were a little contracted. Their structure in this specimen could be

made out (Pl. 24, fig. 1) with perfect distinctness. Their transparent

outer tunic (_e_, fig. 1) is 1/2000ths of an inch in thickness, and is

continuous with that (_d_) enveloping the whole body, but is abruptly

and considerably thicker than this membrane; and hence a very slight

collar is formed outside, round the line of junction of each thread

with the body. The delicate corium (_c_) lining the external membrane

of the body runs, at least someway, down these threads. It was likewise

indisputably evident that the membrane (_b_), for I separated it by

dissection, forming the great ovarian sack, together with the cellular

contents of this sack (_a_), entered and extended down both threads.

It should, also, be particularly observed, that the coarsely cellular

matter within the ovarian sack, immediately that it entered the tube

formed by the membrane of the ovarian sack, suddenly changed its

appearance into a homogeneous, stiff, pulpy matter, which retained the

same appearance all down the threads to within the antennæ. This finer

matter readily separated from the coarser cellular matter within the

sack, but was not divided from it by any septum or membrane. Some way

within the threads, the corium, the membrane of the ovarian sack, and

the contents appear (_e′_), as seen from the outside, to become, and

perhaps really are, blended together. These threads could not have

been originally formed of their present length, and must therefore

have been added to during the growth of the animal; but from their

entering the not-moulted antennæ, and from the animal being permanently

attached by them, they cannot have grown, by means of the moulting of

their integuments; hence I conclude that at each period of growth and

exuviation they have been added to only at their upper ends, where

there is a sort of collar, or line of growth; and where, I may remark,

the lining corium is alone well developed. We shall presently see the

bearing of these remarks.

These threads contract to about half their former diameter as they

enter the old prehensile antennæ of the pupa, within which they are

firmly attached. Each thread, with its three tunics apparently blended

together, can be traced to the extremity of the disc-segment (_g_),

where the included matter seems to have burst forth. The whole disc and

the terminal segment of both antennæ are enveloped, close together,

in cement, formed into two almost separate little capsules, by which

they adhere very firmly to the integuments of the Alepas. The cement

required to be removed before the antennæ could be plainly seen. The

cement presented all the usual characters, namely, its homogeneous

laminated structure and its yellowish colour. The cement in the case

of the male Ibla, which is parasitic within the sack of the female

Ibla, affects the corium and fibrous matter beneath the chitine-tunic,

and causes them to adhere together, and thus prevents the male from

being cast off each time that the inner tunic of the sack of the female

is moulted: exactly so has the cement of the Proteolepas affected

the integuments of the Alepas. The only difference between ordinary

cement-ducts and the two threads here described is, that the ducts,

in both cases formed by the prolongation of the coat of an ovarian

receptacle, are here protected by a thick outer membrane, lined, at

least in the upper part, by corium; whereas, in the Lepadidæ the two

ducts are included within the peduncle, and are therefore protected by

one common membrane, lined of course by corium; and this membrane, we

shall presently see, is homologous with that separately investing the

two threads.

The antennæ differ remarkably little, considering the anomalous

character of the mature animal, from the same organ in other genera;

they come nearest, perhaps, to the antennæ of Ibla. The length of the

disc (_g_, fig. 1) and great succeeding segment (_f_) together is

40/6000ths of an inch. The lower segment has its basal articulation

only slightly oblique, showing that, as in Alcippe and Ibla, it was

probably articulated near the anterior end of the pupal shell: it is

of nearly the same width throughout.[154] The disc (_g_) is remarkable

from its great proportional length; it is hoof-shaped, with the outer

side rather protuberant, and the end pointed. The ultimate segment

(_h_) is of moderate size: as in Ibla, it has a shoulder or notch on

its inner side near its end, bearing two long spines; and probably

there were originally three or four spines on the square broad upper

end, but these have been broken. This segment is articulated unusually

near to the end of the disc.

[154] As I have given the measurements of the antennæ in so many

genera, I will give these: second (_f_, fig. 1) segment, 24/6000ths

of an inch in length, and (8-9)/6000ths in width. Disc, 16/6000ths

in length, and 8/6000ths in width. Ultimate segment, 6/6000ths (?)

in length, and 10/20,000ths (?) in breadth.

The foregoing remarks on the two threads by which Proteolepas is

attached, are, independently of their relation to this individual

animal, of considerable interest. In my volume on the Lepadidæ, I have

stated, after repeated and rigorous examinations (for I was well aware

how singular the facts were), that in _Conchoderma aurita_ and in

some other genera, the cement-ducts, which entered the pupal antennæ,

could be traced till they joined a gland, the coat of which gland was

absolutely continuous with the coats of the adjoining and continuous

ovarian tubes, of which it was only a modified portion; and what was

still more remarkable, that the matter within the gland was continuous

with, and differed only from, the cellular matter within the ovarian

tubes and cæca (from which ova were in the act of formation), by being

more homogeneous and more coherent. Furthermore, I have shown, that

in Ibla an ovarian tube, becomes by a very small change, namely, by

a double flexure and slight thickening of its coat, converted into a

gland, and thus acquires the power of affecting the cellular ovarian

matter and changing it into cement. Now, in Proteolepas, the great

ovarian sack replaces the ovarian tubes and cæca; and we here see

the very same relations even still more plainly; for the coat of the

ovarian sack is indisputably continuous with that investing or forming

the two cement-ducts within the two threads; and immediately that

the coarse cellular matter, which within the ovarian sack is being

converted into ova, enters the upper contracted end of the cement-duct,

by some power, we must suppose, inherent in its coat, it is converted

into cement, which debouches with all its usual properties through the

pupal antennæ. I may venture to reaffirm that nothing could be plainer

than this structure, or be in more striking conformity with my previous

observations, given in the introduction to the Lepadidæ.

* * * * *

I can hardly express the perplexity which I felt when I first examined

Proteolepas, and when I naturally mistook the mouth for the entire

head, for I saw, as I thought, the antennæ in direct connection with

the second segment of the body, posteriorly to the mouth! It was quite

as monstrous and incredible an inversion of the laws of nature, as

those fabulous half-human monsters, with an eye seated in the middle

of their stomachs. After a time, I perceived that the following

considerations removed all difficulty, and brought Proteolepas into the

type of other cirripedes.

_Firstly_: in ordinary cirripedes, the two cement-ducts can be traced

up from the cemented antennæ to the glands, formed by a part of the

ovarian branching cæca; and the latter can be traced to where they

enter, as two simple tubes, the body of the animal, at a medio-dorsal

point, a little anteriorly to the prosoma, or second thoracic

segment.[155] From what is actually seen in the complemental male

of _Scalpellum Peronii_, and from what may be inferred from the

structure of these parts in the pupæ of all cirripedes, there can be

no doubt that if the ovarian cæca were in any case not developed, the

cement-ducts would enter the body at the spot where the two simple

ovarian tubes, which serve to unite the ovarian cæca with the true

ovaria, do enter. Now if we look at the drawing (Pl. 25, fig. 7) of

Proteolepas, we shall see that the cement-ducts enter the body at a

medio-dorsal point, a little anteriorly to the second thoracic segment,

and therefore in the normal position.

[155] This may be partially seen in the section, fig. 1, of

Balanus, on the same plate (25) with the figure of Proteolepas;

here (bearing in mind that Balanus is a much modified form)

(_z_) shows the pupal antennæ, within which, whilst young, the

cement-ducts are included, and are directly continuous with the

layer of branching ovarian cæca (_g_), which are prolonged up

to the ovaria as a pair of simple tubes (only one being here

represented), entering the body above the upper margin of the

prosoma (_c_). The prosoma of Balanus, I may add, answers to

the segment ^2 _t_ in fig. 7 of Proteolepas; (_e_) the mouth

in Balanus, of course corresponding with (_m_) the mouth of

Proteolepas; the segment ^1 _c_ and ^2 _t_ of the latter, are in

Balanus aborted or confluent, at least on the ventral surface; and,

lastly, the whole great shell of Balanus, the sack with its muscles

and the branchiæ, and the opercular valves with their muscles, are

all represented in Proteolepas merely by the outer membrane of the

two threads (_g_), which enter the pupal antennæ!

_Secondly_: the external membrane of the two threads, investing the two

cement-ducts, it should be remembered, is not moulted, and is added to

during growth (being lined internally by corium), only round the upper,

collar-like edge.

_Thirdly_: the external covering or carapace of every young cirripede,

at the period of its metamorphosis, enters, at its lower end, the

cemented antennæ, in the form of two short tubular prolongations,

by which alone, at first, the cirripede adheres to the surface of

attachment; within these prolongations the cement-ducts are included. I

have, moreover, seen instances, as in _Conchoderma aurita_ and in the

male of Ibla and Alcippe, in which these tubular prolongations, lined

internally by corium, were increased a little in length, so as to form

a trouser-like termination to the peduncle. That the forked extremity

should be a little more developed, and so be converted into a pair of

short tubular threads, cannot be considered as very improbable.

_Fourthly_: in the male Ibla the capitulum is so much atrophied that it

does not enclose the thorax or mouth, but still an elongated support or

peduncle is left. But it would be no very violent assumption to imagine

the peduncle, which does not essentially differ from the capitulum, to

become likewise rudimental,--to grow smaller and smaller, and shorter

and shorter, till the merest remnant was left at the spot where it

entered the cemented antennæ. And in the last paragraph it has been

shown that it would be no violent assumption to imagine this lower end

of the peduncle, where it enters the antennæ, developed into two short

thread-like prolongations.

_Lastly_: it is certain, from the existence of the prehensile antennæ,

that Proteolepas was developed within a pupa, probably differing in no

very essential respect from the pupæ of other cirripedes. Therefore, in

accordance with all analogy, we may believe that the position[156] of

the young Proteolepas (probably much coiled up, with a deep fold close

under the mouth) within the pupa, the general form and structure of

the latter, and the course of the cement-ducts, did not _essentially_

differ from the imaginary figure given, Pl. 25, fig. 6. Now, at the

period of the metamorphosis, let us imagine that no general covering

or carapace was formed, except a small portion on the ventral surface,

round the cemented antennæ. Let us further suppose this remnant to be

specially developed (as in the case of some cirripedes) into a short

trouser-like prolongation, entering the antennæ; and subsequently, in

accordance with the almost universal laws of growth in cirripedes, that

this portion was never moulted, but continued to be added to, during

growth, only at its upper end. By this means we should produce every

leading peculiarity of the _Proteolepas bivincta_. As this parasite

lives within the sack of another cirripede, and is protected by the

capitulum of the latter, we can understand, in accordance with the

usual admirable economy of nature, the absence of any general covering

for its body. We can now, also, understand the structure and manner of

growth of the two threads by which it is bound to its prey; and the

connection, at first so strange and perplexing, between the old pupal

antennæ and the second segment of the thorax. I am convinced that no

other explanation than that here given, will accord with the relations

of the several parts and organs of Proteolepas. Consequently, I fully

believe that we here see an articulate animal in which the whole of

the three anterior segments of the head have been, during the act

of metamorphosis, absolutely aborted, with the exception of a mere

rudiment on the ventral surface, near the anterior end, round the old

antennæ, and which rudiment has been specially developed as a covering

for the two cement-ducts. As the pupal antennæ are, homologically, the

second pair of antennæ, we may further infer that this modified remnant

of the carapace, investing the two threads, belongs to the third

cephalic segment.

[156] Any one who has not specially attended to the metamorphoses

of ordinary cirripedes, who looks at the imaginary figure of

the young Proteolepas, will feel much surprise at the relative

positions of the parts; for the mouth and the first and even

second segments of the body stand posteriorly (_i. e._ above in

the figure) to the succeeding segments of the body, in relation to

the carapace of the pupa; but this is only in accordance with the

remarkable change in position (as explained in the introduction,

p. 123, pl. 30, fig. 2), amounting almost to inversion, which the

whole thorax of every young cirripede undergoes within the pupa,

whilst the anterior cephalic portions and general covering are

developed conformably with the pupal carapace, whence it arises

that the _dorsal_ surface of that part of the thorax immediately

succeeding the mouth becomes attached to the _ventral_ internal

surface of the carapace. I believe that the peculiar flattened

dorsal outline of the first two segments of the body of Proteolepas

is due to these parts having been formed in contact (as represented

in pl. 25, fig. 6) with the straight ventral surface of the

carapace of the pupa. To place the young Proteolepas, and at the

same time the carapace of the pupa, with all the parts in proper

homological sequence, it would be necessary to seize the posterior

end of the abdomen (_a_), and pull till the dorsal surfaces of the

first and second segments of the body, separated from the ventral

internal surface of the carapace, and stood posteriorly (_i. e._

above in figure) to the mouth, which latter would thus also have to

rotate a quarter of a circle, so that the orifice would come to be

directed outwards. Then every part would stand, in accordance with

the archetype crustacean structure, in due order; but the three

confluent anterior cephalic segments, forming the front part and

carapace of the pupa, would, as in the case of all cirripedes, be

of disproportionately large size in relation to the rest of the

body.