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SEASIDE STUDIES
IN
NATURAL HISTORY.
BY
ELIZABETH C. AGASSIZ
AND
ALEXANDER AGASSIZ.
MARINE ANIMALS OF MASSACHUSETTS BAY.
RADIATES.
[Illustration]
BOSTON:
JAMES R. OSGOOD AND COMPANY,
LATE TICKNOR & FIELDS, AND FIELDS, OSGOOD, & CO.
1871.
Entered according to Act of Congress, in the year 1865, by
A L E X A N D E R A G A S S I Z,
in the Clerk's Office of the District Court
for the District of Massachusetts.
UNIVERSITY PRESS:
WELCH, BIGELOW, AND COMPANY,
CAMBRIDGE.
THIS LITTLE BOOK
IS AFFECTIONATELY DEDICATED BY THE AUTHORS TO
PROFESSOR L. AGASSIZ,
WHOSE PRINCIPLES OF CLASSIFICATION HAVE BEEN THE MAIN
GUIDE IN ITS PREPARATION.
* * * * *
PREFACE.
This volume is published with the hope of supplying a want often
expressed for some seaside book of a popular character, describing the
marine animals common to our shores. There are many English books of
this kind; but they relate chiefly to the animals of Great Britain,
and can only have a general bearing on those of our own coast, which
are for the most part specifically different from their European
relatives. While keeping this object in view, an attempt has also been
made to present the facts in such a connection, with reference to
principles of science and to classification, as will give it in some
sort the character of a manual of Natural History, in the hope of
making it useful not only to the general reader, but also to teachers
and to persons desirous of obtaining a more intimate knowledge of the
subjects discussed in it. With this purpose, although nearly all the
illustrations are taken from among the most common inhabitants of our
bay, a few have been added from other localities in order to fill out
this little sketch of Radiates, and render it, as far as is possible
within such limits, a complete picture of the type.
A few words of explanation are necessary with reference to the joint
authorship of the book. The drawings and the investigations, where
they are not referred to other observers, have been made by MR. A.
AGASSIZ, the illustrations having been taken, with very few
exceptions, from nature, in order to represent the animals, as far as
possible, in their natural attitudes; and the text has been written by
MRS. L. AGASSIZ, with the assistance of MR. A. AGASSIZ's notes and
explanations.
CAMBRIDGE, May, 1865.
* * * * *
NOTE.
This second edition is a mere reprint of the first. A few mistakes
accidentally overlooked have been corrected; an explanation of the
abbreviations of the names of writers used after the scientific names
has been added, as well as a list of the wood-cuts. The changes which
have taken place in the opinions of scientific men with regard to the
distribution of animal life in the ocean have been duly noticed in
their appropriate place, but no attempt has been made to incorporate
more important additions which the progress of our knowledge of
Radiates may require hereafter.
CAMBRIDGE, January, 1871.
* * * * *
CONTENTS.
PAGE
ON RADIATES IN GENERAL 1
GENERAL SKETCH OF THE POLYPS 5
ACTINOIDS 7
MADREPORIANS 16
HALCYONOIDS 19
GENERAL SKETCH OF ACALEPHS 21
CTENOPHORÆ 26
EMBRYOLOGY OF CTENOPHORÆ 34
DISCOPHORÆ 37
HYDROIDS 49
MODE OF CATCHING JELLY-FISHES 85
ECHINODERMS 91
HOLOTHURIANS 95
ECHINOIDS 101
STAR-FISHES 108
OPHIURANS 115
CRINOIDS 120
EMBRYOLOGY OF ECHINODERMS 123
DISTRIBUTION OF LIFE IN THE OCEAN 141
SYSTEMATIC TABLE 152
INDEX 154
LIST OF THE WOOD-CUTS.
Unless otherwise specified, the illustrations are drawn from nature
by ALEX. AGASSIZ.
FIG. PAGE
1. Transverse section of an Actinia (Agassiz) 5
2, 3, 4. Actinia in different degrees of expansion (Agassiz) 8
5. METRIDIUM MARGINATUM fully expanded 8
6. Vertical section of an Actinia 10
7. View from above of an expanded Actinia 11
8, 9. Young Actiniæ 11
10. RHODACTINIA DAVISII 13
11. ARACHNACTIS BRACHIOLATA 14
12. Young Arachnactis 14
13. Young Arachnactis showing the mouth 14
14. BICIDIUM PARASITICUM 15
15. HALCAMPA ALBIDA 16
16. Colony of ASTRANGIA DANÆ 17
17. Magnified individuals of Astrangia 17
18. Single individual of Astrangia 18
19. Lasso-cell of Astrangia 18
20. Limestone pit of Astrangia 19
21. Single individual of HALCYONIUM CARNEUM 19
22. Halcyonium community 20
23. Expanded individual of Halcyonium 20
24. Branch of MILLEPORA ALCICORNIS (Agassiz) 22
25. Expanded animals of Millepora (Agassiz) 22
26. Transverse section of branch of Millepora (Agassiz) 23
27. PLEUROBRACHIA RHODODACTYLA (Agassiz) 27
28. The same as Fig. 27 seen in plane of tentacles (Agassiz) 28
29. Pleurobrachia in motion 29
30. Pleurobrachia seen from the extremity opposite the mouth 30
31. BOLINA ALATA seen from the broad side (Agassiz) 31
32. Bolina seen from the narrow side (Agassiz) 31
33. IDYIA ROSEOLA seen from the broad side (Agassiz) 32
34. Young Pleurobrachia still in the egg 35
35. Young Pleurobrachia swimming in the egg 35
36. Young Pleurobrachia resembling already adult 35
37. Young Idyia 35
38. Young Idyia seen from the anal pole 36
39. Idyia somewhat older than Fig. 37 36
40. Idyia still older 36
41. Young Bolina in stage resembling Pleurobrachia 37
42. Young Bolina seen from the broad side 37
43. Young Bolina seen from the narrow side 37
44. CYANEA ARCTICA 40
45. Scyphistoma of Aurelia (Agassiz) 41
46. Scyphistoma older than Fig. 45 (Agassiz) 41
47. Strobila of Aurelia (Agassiz) 41
48. Ephyra of Aurelia (Agassiz) 42
49. AURELIA FLAVIDULA seen in profile (Agassiz) 42
50. Aurelia seen from above (Agassiz) 43
51. CAMPANELLA PACHYDERMA 44
52. The same from below 44
53. TRACHYNEMA DIGITALE 45
54. HALICLYSTUS AURICULA 46
55. Lucernaria seen from the mouth side 47
56. Young Lucernaria 48
57. Hydrarium of EUCOPE DIAPHANA 50
58. Magnified portion of Fig. 57 50
59. Part of marginal tentacles of Eucope 51
60. Young Eucope 51
61. Adult Eucope, profile 51
62. Quarter-disk of Fig. 60 51
63. Quarter-disk of Eucope older than Fig. 62 52
64. Quarter-disk of adult Eucope 52
65. OCEANIA LANGUIDA just escaped from the reproductive calycle 53
66. Same as Fig. 65 from below 53
67. Young Oceania older than Fig. 65 54
Diagram of succession of tentacles 54
68. Adult Oceania 55
69. Attitude assumed by Oceania 56
70. CLYTIA BICOPHORA escaped from reproductive calycle 57
71. Somewhat older than Fig. 70 57
72. Magnified portion of Hydrarium of Clytia 57
73. Adult Clytia 57
74. ZYGODACTYLA GROENLANDICA 58
75. The same seen in profile 59
76. TIMA FORMOSA 61
77. One of the lips of the mouth 61
78. Head of Hydrarium of Tima 62
79. MELICERTUM CAMPANULA from above (Agassiz) 63
80. The same seen in profile 64
81. Planula of Melicertum 65
82. Cluster of planulæ 65
83. Young Hydrarium 65
84. DYNAMENA PUMILA 66
85. Magnified portion of Fig. 84 66
86. DYPHASIA ROSACEA 67
87. Medusa of LAFOEA 67
88. Colony of Coryne mirabilis (Agassiz) 68
89. Magnified head of Fig. 88 (Agassiz) 68
90. Free Medusa of Coryne (Agassiz) 68
91. TURRIS VESICARIA 69
92. BOUGAINVILLIA SUPERCILIARIS 70
93. Hydrarium of Bougainvillia 70
94, 95, 96. Medusæ buds of Fig. 93 71
97. Young Medusa just freed from the Hydroid 71
98. TUBULARIA COUTHOUYI (Agassiz) 72
99. Cluster of Medusæ of Fig. 98 (Agassiz) 72
100. Female colony of HYDRACTINIA POLYCLINA (Agassiz) 73
101. Male colony of the same (Agassiz) 73
102. Unsymmetrical Medusa of HYBOCODON PROLIFER (Agassiz) 74
103. Medusa bud of Hybocodon (Agassiz) 74
104. Hybocodon Hydrarium (Agassiz) 74
105. DYSMORPHOSA FULGURANS 75
106. Proboscis of Fig. 105 with young Medusæ 75
107. Young NANOMIA CARA 76
108. Nanomia with rudimentary Medusæ 76
109. Nanomia somewhat older than Fig. 108 77
110. Heart-shaped swimming bell of Nanomia 77
111. Cluster of Medusæ with tentacles having pendent knobs 78
112. Magnified pendent knob 79
113. Medusa with corkscrew-shaped tentacles 79
114. Medusa with simple tentacle 80
115. Adult Nanomia 81
116. Oil float of Nanomia 82
117. PHYSALIA ARETHUSA (Agassiz) 83
118. Bunch of Hydræ (Agassiz) 84
119. Cluster of Medusæ (Agassiz) 86
120. VELELLA MUTICA (Agassiz) 84
121. Free Medusa of Velella (Agassiz) 84
122. PTYCHOGENA LACTEA 86
123. Ovary of Ptychogena 87
124. SYNAPTA TENUIS 95
125. Anchor of Synapta 96
126. CAUDINA ARENATA 97
127. CUVIERIA SQUAMATA 98
128. Young Cuvieria 99
129. Cuvieria somewhat older than Fig. 128 99
130. PENTACTA FRONDOSA 100
131. TOXOPNEUSTES DROBACHIENSIS 102
132. Portion of shell of Fig. 131 without spines (Agassiz) 103
133. Sea-urchin shell without spines (Agassiz) 103
134. Sea-urchin from the mouth side (Agassiz) 104
135. Magnified spine 104
136. Transverse section of spine 105
137. Pedicellaria of Sea-urchin 105
138. Teeth of Sea-urchin 106
139. ECHINARACHNIUS PARMA 107
140. Transverse section of Echinarachnius (Agassiz) 108
141. Ray of Star-fish, seen from mouth side (Agassiz) 109
142. ASTRACANTHION BERYLINUS 110
143. Single spine of Star-fish 111
144. Limestone network of back of Star-fish 111
145. Madreporic body of Star-fish 111
146. CRIBRELLA OCULATA 112
147. CTENODISCUS CRISPATUS 114
148. OPHIOPHOLIS BELLIS 115
149. Arm of Fig. 148, from the mouth side (Agassiz) 116
150. Tentacle of Ophiopolis 116
151. ASTROPHYTON AGASSIZII 118
152. Pentacrinus 121
153. ALECTO MERIDIONALIS 122
154. Young Comatulæ 122
155, 156, 157. Egg of Star-fish in different stages
of development 124
158. Larva just hatched from egg 125
159-164. Successive stages of development of Larva 125
165. Larva in which arms are developing 126
166. Adult Star-fish Larva (BRACHIOLARIA) 127
167. Fig. 166 seen in profile 128
168-170. Young Star-fish (Astracanthion) in different stages
of development 129
171. Lower side of ray of young Star-fish 130
172. Very young Star-fish seen in profile 130
173-175. Larvæ of Sea-urchin (Toxopneustes) in different stages
of development 130, 131
176. Adult Larva of Sea-urchin 132
177. Fig. 176 seen endways 133
178. Sea-urchin resorbing the arms of the larva 133
179-181. Successive stages of young Sea-urchin 133, 134
182. Ophiuran which has nearly resorbed the larva 135
183. Larva of Ophiuran (Pluteus) 136
184. Young Ophiuran 137
185. Cluster of eggs of Star-fishes over mouth of parent 137
Diagram of a rocky beach 149
ABBREVIATIONS OF THE NAMES OF AUTHORS.
AG. L. Agassiz.
A. AG. A. Agassiz.
AYRES W. O. Ayres.
BLAINV. Blainville.
BOSC Bosc.
BR. Brandt.
CLARK H. J. Clark.
CUV. Cuvier.
D. & K. Düben and Koren.
EDW. Milne-Edwards.
FORBES Edw. Forbes.
GRAY J. E. Gray.
JAEG. Jaeger.
LAM. Lamarck.
LAMX. Lamouroux.
LIN. Linnæus.
LYM. Lyman.
M. & T. Müller and Troschel.
MILL. Miller.
PÉR. et LES. Péron and Lesueur.
SARS M. Sars.
STIMP. Stimpson.
TIL. Tilesius.
* * * * *
MARINE ANIMALS OF MASSACHUSETTS BAY.
ON RADIATES IN GENERAL.
It is perhaps not strange that the Radiates, a type of animals whose
home is in the sea, many of whom are so diminutive in size, and so
light and evanescent in substance, that they are hardly to be
distinguished from the element in which they live, should have been
among the last to attract the attention of naturalists. Neither is it
surprising to those who know something of the history of these
animals, that when the investigation of their structure was once
begun, when some insight was gained into their complex life, their
association in fixed or floating communities, their wonderful
processes of development uniting the most dissimilar individuals in
one and the same cycle of growth, their study should have become one
of the most fascinating pursuits of modern science, and have engaged
the attention of some of the most original investigators during the
last half century. It is true that from the earliest days of Natural
History, the more conspicuous and easily accessible of these animals
attracted notice and found their way into the scientific works of the
time. Even Aristotle describes some of them under the names of
Acalephæ and Knidæ, and later observers have added something, here and
there, to our knowledge on the subject; but it is only within the last
fifty years that their complicated history has been unravelled, and
the facts concerning them presented in their true connection.
Among the earlier writers on this subject we are most indebted to
Rondelet, in the sixteenth century, who includes some account of the
Radiates, in his work on the marine animals of the Mediterranean. His
position as Professor in the University at Montpelier gave him an
admirable opportunity, of which he availed himself to the utmost, for
carrying out his investigations in this direction. Seba and Klein, two
naturalists in the North of Europe, also published at about this time
numerous illustrations of marine animals, including Radiates. But in
all these works we find only drawings and descriptions of the animals,
without any attempt to classify them according to common structural
features. In 1776, O. F. Müller, in a work on the marine and
terrestrial faunæ of Denmark, gave some admirable figures of Radiates,
several of which are identical with those found on our own coast.
Cavolini also in his investigations on the lower marine animals of the
Mediterranean, and Ellis in his work upon those of the British coast,
did much during the latter half of the past century to enlarge our
knowledge of them.
It was Cuvier, however, who first gave coherence and precision to all
previous investigations upon this subject, by showing that these
animals are united on a common plan of structure expressively
designated by him under the name Radiata. Although, from a mistaken
appreciation of their affinities, he associated some animals with them
which do not belong to the type, and have since, upon a more intimate
knowledge of their structure, been removed to their true positions;
yet the principle introduced by him into their classification, as well
as into that of the other types of the animal kingdom, has been all
important to science.
It was in the early part of this century that the French began to
associate scientific objects with their government expeditions.
Scarcely any important voyage was undertaken to foreign countries by
the French navy which did not include its corps of naturalists, under
the patronage of government. Among the most beautiful figures we have
of Radiates, are those made by Savigny, one of the French naturalists
who accompanied Napoleon to Egypt; and from this time the lower marine
animals began to be extensively collected and studied in their living
condition. Henceforth the number of investigators in the field became
more numerous, and it may not be amiss to give here a slight account
of the more prominent among them.
Darwin's fascinating book, published after his voyage to the Pacific,
and giving an account of the Coral islands, the many memoirs of Milne
Edwards and Haime, and the great works of Quoy and Gaimard, and of
Dana, are the chief authorities upon Polyps. In the study of the
European Acalephs we have a long list of names high in the annals of
science. Eschscholtz, Péron and Lesueur, Quoy and Gaimard, Lesson,
Mertens, and Huxley, have all added largely to our information
respecting these animals, their various voyages having enabled them to
extend their investigations over a wide field. No less valuable have
been the memoirs of Kölliker, Leuckart, Gegenbaur, Vogt, and Haeckel,
who in their frequent excursions to the coasts of Italy and France
have made a special study of the Acalephs, and whose descriptions have
all the vividness and freshness which nothing but familiarity with the
living specimens can give. Besides these, we have the admirable works
of Von Siebold, of Ehrenberg, the great interpreter of the microscopic
world, of Steenstrup, Dujardin, Dalyell, Forbes, Allman, and Sars. Of
these, the four latter were fortunate in having their home on the
sea-shore within reach of the objects of their study, so that they
could watch them in their living condition, and follow all their
changes. The charming books of Forbes, who knew so well how to
popularize his instructions, and present scientific results under the
most attractive form, are well known to English readers. But a word on
the investigations of Sars may not be superfluous.
Born near the coast of Norway, and in early life associated with the
Church, his passion for Natural History led him to employ all his
spare time in the study of the marine animals immediately about him,
and his first papers on this subject attracted so much attention, that
he was offered the place of Professor at Christiania, and henceforth
devoted himself exclusively to scientific pursuits, and especially to
the investigation of the Acalephs. He gave us the key to the almost
fabulous transformations of these animals, and opened a new path in
science by showing the singular phenomenon of the so-called "alternate
generations," in which the different phases of the same life may be so
distinct and seemingly so disconnected that, until we find the
relation between them, we seem to have several animals where we have
but one.
To the works above mentioned, we may add the third and fourth volumes
of Professor Agassiz's Contributions to the Natural History of the
United States, which are entirely devoted to the American Acalephs.
The most important works and memoirs concerning the Echinoderms are
those by Klein, Link, Johannes Müller, Jäger, Desmoulins, Troschel,
Sars, Savigny, Forbes, Agassiz, and Lütken, but excepting those of
Forbes and Sars, few of these observations are made upon the living
specimens. It may be well to mention here, for the benefit of those
who care to know something more of the literature of this subject in
our own country, a number of memoirs on the Radiates of our coasts,
published by the various scientific societies of the United States,
and to be found in their annals. Such are the papers of Gould,
Agassiz, Leidy, Stimpson, Ayres, McCrady, Clark, A. Agassiz, and
Verrill.
One additional word as to the manner in which the subjects included in
the following descriptions are arranged. We have seen that Cuvier
recognized the unity of plan in the structure of the whole type of
Radiates. All these animals have their parts disposed around a common
central axis, and diverging from it toward the periphery. The idea of
bilateral symmetry, or the arrangement of parts on either side of a
longitudinal axis, on which all the higher animals are built, does not
enter into their structure, except in a very subordinate manner,
hardly to be perceived by any but the professional naturalist. This
radiate structure being then common to the whole type, the animals
composing it appear under three distinct structural expressions of the
general plan, and according to these differences are divided into
three classes,--Polyps, Acalephs, and Echinoderms. With these few
preliminary remarks we may now take up in turn these different groups,
beginning with the lowest, or the Polyps.[1]
[Footnote 1: It is to be regretted that on account of the meagre
representations of Polyps on our coast, where the coral reefs, which
include the most interesting features of Polyp life, are entirely
wanting, our account of these animals is necessarily deficient in
variety of material. When we reach the Acalephs or Jelly-Fishes, in
which the fauna of our shores is especially rich, we shall not have the
same apology for dulness; and it will be our own fault if our readers
are not attracted by the many graceful forms to which we shall then
introduce them.]
* * * * *
GENERAL SKETCH OF THE POLYPS.
Before describing the different kinds of Polyps living on our
immediate coast, we will say a few words of Polyps in general and of
the mode in which the structural plan common to all Radiates is
adapted to this particular class. In all Polyps the body consists of a
sac divided by vertical partitions (Fig. 1.) into distinct cavities or
chambers. These partitions are not, however, all formed at once, but
are usually limited to six at first, multiplying indefinitely with the
growth of the animal in some kinds, while in others they never
increase beyond a certain definite number. In the axis of the sac,
thus divided, hangs a smaller one, forming the digestive cavity, and
supported for its whole length by the six primary partitions. The
other partitions, though they extend more or less inward in proportion
to their age, do not unite with the digestive sac, but leave a free
space in the centre between their inner edge and the outer wall of the
digestive sac. The genital organs are placed on the inner edges of the
partitions, thus hanging as it were at the door of the chambers, so
that when hatched, the eggs naturally drop into the main cavity of the
body, whence they pass into the second smaller sac through an opening
in its bottom or digestive cavity, and thence out through the mouth
into the water. In the lower Polyps, as in our common Actinia for
instance, these organs occur on all the radiating partitions, while
among the higher ones, the Halcyonoids for example, they are found
only on a limited number. This limitation in the repetition of
identical parts is always found to be connected with structural
superiority.
[Illustration: Fig. 1. Transverse section of an Actinia.
(_Agassiz_.)]
The upper margin of the body is fringed by hollow tentacles, each of
which opens into one of the chambers. All parts of the animal thus
communicate with each other, whatever is introduced at the mouth
circulating through the whole structure, passing first into the
digestive cavity, thence through the opening in the bottom into the
main chambered cavity, where it enters freely into all the chambers,
and from the chambers into the tentacles. The rejected portions of the
food, after the process of digestion is completed, return by the same
road and are thrown out at the mouth.
These general features exist in all Polyps, and whether they lead an
independent life as the Actinia, or are combined in communities, like
most of the corals and the Halcyonoids; whether the tentacles are many
or few; whether the partitions extend to a greater or less height in the
body; whether they contain limestone deposit, as in the corals, or
remain soft throughout life as the sea-anemone,--the above description
applies to them all, while the minor differences, either in the
tentacles or in the form, size, color, and texture of the body, are
simply modifications of this structure, introducing an infinite variety
into the class, and breaking it up into the lesser groups designated as
orders, families, genera, and species. Let us now look at some of the
divisions thus established.
The class of Polyps is divided into three orders,--the Halcyonoids,
the Madreporians, and the Actinoids. Of the lowest among these orders,
the Actinoid Polyps, our Actinia or sea-anemone is a good example.
They remain soft through life, having a great number of partitions and
consequently a great number of tentacles, since there is a tentacle
corresponding to every chamber. Indeed, in this order the
multiplication of tentacles and partitions is indefinite, increasing
during the whole life of the animal with its growth; while we shall
see that in some of the higher orders the constancy and limitation in
the number of these parts is an indication of superiority, being
accompanied by a more marked individualization of the different
functions.
Next come the Madreporians, of which our Astrangia, to be described
hereafter, may be cited as an example. In this group, although the
number of tentacles still continues to be large, they are nevertheless
more limited than in the Actinoids; but their characteristic feature
is the deposition of limestone walls in the centre of the chambers
formed by the soft partitions, so that all the soft partitions
alternate with hard ones. The tentacles, always corresponding to the
cavity of the chambers, may be therefore said to ride this second set
of partitions arising just in the centre of the chambers.
The third and highest order of Polyps is that of the Halcyonoids. Here
the partitions are reduced to eight; the tentacles, according to the
invariable rule, agree in number with the chambers, but have a far
more highly complicated structure than in the lower Polyps. Some of
these Halcyonoids deposit limestone particles in their frame. But the
tendency to solidify is not limited to definite points, as in the
Madreporians. It may take place anywhere, the rigidity of the whole
structure increasing of course in proportion to the accumulation of
limestone. There are many kinds, in which the axis always remains soft
or cartilaginous, while others, as the so-called sea-fans for
instance, well known among the corals for their beauty of form and
color, are stiff and hard throughout. Whatever their character in this
respect, however, they are always compound, living in communities, and
never found as separate individuals after their early stages of
growth. Some of those with soft axis lead a wandering life, enjoying
as much freedom of movement as if they had an individual existence,
shooting through the water like the Pennatulæ, well known on the
California coast, or working their way through the sand like the
Renilla, common on the sandy shores of our Southern States.
* * * * *
ACTINOIDS.
_Actinia, or Sea-Anemone_. (_Metridium marginatum_ EDW.)
Nothing can be more unprepossessing than a sea-anemone when
contracted. A mere lump of brown or whitish jelly, it lies like a
lifeless thing on the rock to which it clings, and it is difficult to
believe that it has an elaborate and exceedingly delicate internal
organization, or will ever expand into such grace and beauty as really
to deserve the name of the flower after which it has been called.
Figs. 2, 3, 4, and 5, show this animal in its various stages of
expansion and contraction. Fig. 2 represents it with all its external
appendages folded in, and the whole body flattened; in Fig. 3, the
tentacles begin to steal out, and the body rises slightly; in Fig. 4,
the body has nearly gained its full height, and the tentacles, though
by no means fully spread, yet form a delicate wreath around the mouth;
while in Fig. 5, drawn in life size, the whole summit of the body
seems crowned with soft, plumy fringes. We would say for the benefit
of collectors that these animals are by no means difficult to find,
and thrive well in confinement, though it will not do to keep them in
a small aquarium with other specimens, because they soon render the
water foul and unfit for their companions. They should therefore be
kept in a separate glass jar or bowl, and under such circumstances
will live for a long time with comparatively little care.
[Illustration: Figs. 2, 3, 4. Actinia in different degrees of
expansion. (_Agassiz_.)]
[Illustration: Fig. 5. The same Actinia (Metridium marginatum)
fully expanded; natural size.]
They may be found in any small pools about the rocks which are flooded
by the tide at high water. Their favorite haunts, however, where they
occur in greatest quantity are more difficult to reach; but the
curious in such matters will be well rewarded, even at the risk of wet
feet and a slippery scramble over rocks covered with damp sea-weed, by
a glimpse into their more crowded abodes. Such a grotto is to be found
on the rocks of East Point at Nahant. It can only be reached at low
tide, and then one is obliged to creep on hands and knees to its
entrance, in order to see through its entire length; but its whole
interior is studded with these animals, and as they are of various
hues, pink, brown, orange, purple, or pure white, the effect is like
that of brightly colored mosaics set in the roof and walls. When the
sun strikes through from the opposite extremity of this grotto, which
is open at both ends, lighting up its living mosaic work, and showing
the play of the soft fringes wherever the animals are open, it would
be difficult to find any artificial grotto to compare with it in
beauty. There is another of the same kind on Saunders's Ledge, formed
by a large boulder resting on two rocky ledges, leaving a little cave
beneath, lined in the same way with variously colored sea-anemones, so
closely studded over its walls that the surface of the rock is
completely hidden. They are, however, to be found in larger or smaller
clusters, or scattered singly in any rocky fissures, overhung by
sea-weed, and accessible to the tide at high water.
The description of Polyp structure given above includes all the
general features of the sea-anemone; but for the better explanation of
the figures, it may not be amiss to recapitulate them here in their
special application. The body of the sea-anemone may be described as a
circular, gelatinous bag, the bottom of which is flat and slightly
spreading around the margin. (Fig. 2.) The upper edge of this bag
turns in so as to form a sac within a sac. (Fig. 6.) This inner sac,
_s_, is the stomach or digestive cavity, forming a simple open space
in the centre of the body, with an aperture in the bottom, _b_,
through which the food passes into the larger sac, in which it is
enclosed. But this outer and larger sac or main cavity of the body is
not, like the inner one, a simple open space. It is, on the contrary,
divided by vertical partitions into a number of distinct chambers,
converging from the periphery to the centre. These partitions do not
all advance so far as actually to join the wall of the digestive
cavity hanging in the centre of the body, but most of them stop a
little short of it, leaving thus a small, open space between the
chambers and the inner sac. (Fig. 1.) The eggs hang on the inner edge
of the partitions; when mature they drop into the main cavity, enter
the inner digestive cavity through its lower opening, and are passed
out through the mouth.
[Illustration: Fig. 6. Vertical section of an Actinia, showing a
primary _(g)_ and a secondary partition of _g'_; _o_ mouth, _t_
tentacles, _s_ stomach, _f f_ reproductive organs, _b_ main
cavity, _c_ openings in partitions, _a_ lower floor, or foot.]
The embryo bears no resemblance to the mature animal. It is a little
planula, semi-transparent, oblong, entirely covered with vibratile
cilia, by means of which it swims freely about in the water till it
establishes itself on some rocky surface, the end by which it becomes
attached spreading slightly and fitting itself to the inequalities of
the rock so as to form a secure basis. The upper end then becomes
depressed toward the centre, that depression deepening more and more
till it forms the inner sac, or in other words the digestive cavity
described above. The open mouth of this inner sac, which may, however,
be closed at will, since the whole substance of the body is
exceedingly contractile, is the oral opening or so-called mouth of the
animal. We have seen how the main cavity becomes divided by radiating
partitions into numerous chambers; but while these internal changes
are going on, corresponding external appendages are forming in the
shape of the tentacles, which add so much to the beauty of the animal,
and play so important a part in its history. The tentacles, at first
only few in number, are in fact so many extensions of the inner
chambers, gradually narrowing upward till they form these delicate
hollow feelers which make a soft downy fringe all around the mouth.
(Fig. 7.) They do not start abruptly from the summit, but the upper
margin of the body itself thins out to form more or less extensive
lobes, through which the partitions and chambers continue their
course, and along the edge of which the tentacles arise.
[Illustration: Fig. 7. View from above of an Actinia with all its
tentacles expanded; _o_ mouth, _b_ crescent-shaped folds at
extremity of mouth, _a a_ folds round mouth, _t t t_ tentacles.]
[Illustration: Figs. 8, 9. Young Actiniæ in different stages of
growth.]
The eggs are not always laid in the condition of the simple planula
described above. They may, on the contrary, be dropped from the parent
in different stages of development, sometimes even after the tentacles
have begun to form, as in Figs. 8, 9. Neither is it by means of eggs
alone that these animals reproduce themselves; they may also multiply
by a process of self-division. The disk of an Actinia may contract
along its centre till the circular outline is changed to that of a
figure 8, this constriction deepening gradually till the two halves of
the 8 separate, and we have an Actinia with two mouths, each
surrounded by an independent set of tentacles. Presently this
separation descends vertically till the body is finally divided from
summit to base, and we have two Actiniæ where there was originally but
one. Another and a far more common mode of reproduction among these
animals is that of budding like corals. A slight swelling arises on
the side of the body or at its base; it enlarges gradually, a
digestive cavity is formed within it, tentacles arise around its
summit, and it finally drops off from the parent and leads an
independent existence. As a number of these buds are frequently formed
at once, such an Actinia, surrounded by its little family, still
attached to the parent, may appear for a time like a compound stock,
though their normal mode of existence is individual and distinct.
The Actinia is exceedingly sensitive, contracting the body and drawing
in the tentacles almost instantaneously at the slightest touch. These
sudden movements are produced by two powerful sets of muscles, running
at right angles with each other through the thickness of the body
wall; the one straight and vertical, extending from the base of the
wall to its summit; the other circular and horizontal, stretching
concentrically around it. By the contraction of the former, the body
is of course shortened; by the contraction of the latter, the body is,
on the contrary, lengthened in proportion to the compression of its
circumference. Both sets can easily be traced by the vertical and
horizontal lines crossing each other on the external wall of the body,
as in Fig. 5. Each tentacle is in like manner furnished with a double
set of muscles, having an action similar to that described above. In
consequence of these violent muscular contractions, the water imbibed
by the animal, and by which all its parts are distended to the utmost,
is forced, not only out of the mouth, but also through small openings
in the body wall scarcely perceptible under ordinary circumstances,
but at such times emitting little fountains in every direction.
Notwithstanding its extraordinary sensitiveness, the organs of the
senses in the Actinia are very inferior, consisting only of a few
pigment cells accumulated at the base of the tentacles. The two sets
of muscles meet at the base of the body, forming a disk, or kind of
foot, by which the animal can fix itself so firmly to the ground, that
it is very difficult to remove it without injury. It is nevertheless
capable of a very limited degree of motion, by means of the expansion
and contraction of this foot-like disk.
The Actiniæ are extremely voracious; they feed on mussels and cockles,
sucking the animals out of their shells. When in confinement they may
be fed on raw meat, and seem to relish it; but if compelled to do so,
they will live on more meagre fare, and will even thrive for a long
time on such food as they may pick up in the water where they are
kept.
_Rhodactinia_ (_Rhodactinia Davisii_ AG.)
[Illustration: Fig. 10. Rhodactinia Davisii Ag.; natural size.]
Very different from this is the bright red Rhodactinia (Fig. 10),
quite common in the deeper waters of our bay, while farther north, in
Maine, it occurs at low-water mark. Occasionally it may be found
thrown up on our sandy beaches after a storm, and then, if it has not
been too long out of its native element, or too severely buffeted by
the waves, it will revive on being thrown into a bucket of fresh
sea-water, expand to its full size, and show all the beauty of its
natural coloring. It is crowned with a wreath of thick, short
tentacles (Fig. 10), and though so vivid and bright in color, it is
not so pretty as the more common Actinia marginata, with its soft
waving wreath of plume-like feelers, in comparison to which the
tentacles of the Rhodactinia are clumsy and slow in their movements.
All Actiniæ are not attached to the soil like those described above,
nor do they all terminate in a muscular foot, some being pointed or
rounded at their extremity. Many are nomadic, wandering about at will
during their whole lifetime, others live buried in the sand or mud,
only extending their tentacles beyond the limits of the hole where
they make their home; while others again lead a parasitic life,
fastening themselves upon our larger jelly-fish, the Cyaneæ, though
one is at a loss to imagine what sustenance they can derive from
animals having so little solidity, and consisting so largely of water.
_Arachnactis_. (_Arachnactis brachiolata_ A. AG.)
[Illustration: Fig. 11. Arachnactis brachiolata A. Ag., greatly
magnified.]
[Illustration: Fig. 12. Young Arachnactis.]
[Illustration: Fig. 13. Young Arachnactis seen so as to show the
mouth.]
Among the nomadic Polyps is a small floating Actinia, called
Arachnactis, (Fig. 11,) from its resemblance to a spider. They are
found in great plenty floating about during the night, feeling their
way in every direction by means of their tentacles, which are large in
proportion to the size of the animal, few in number, and turned
downward when in their natural attitude. The partitions and the
digestive cavity enclosed between them are short, as will be seen in
Fig. 11, when compared to the general cavity of the body floating
balloon-like above them. Around the mouth is a second row of shorter
tentacles, better seen in a younger specimen (Fig. 12). This Actinia
differs from those described above, in having two of the sides
flattened, instead of being perfectly circular. Looked at from above
(as in Fig. 13) this difference in the diameters is very perceptible;
there is an evident tendency towards establishing a longitudinal axis.
In the sea-anemone, this disposition is only hinted at in the slightly
pointed folds or projections on opposite sides of the circle formed by
the mouth, which in the Arachnactis are so elongated as to produce a
somewhat narrow slit (see Fig. 13), instead of a circular opening. The
mouth is also a little out of centre, rather nearer one end of the
disk than the other. These facts are interesting, as showing that the
tendency towards establishing a balance of parts, as between an
anterior and posterior extremity, a right and left side, is not
forgotten in these lower animals, though their organization as a whole
is based upon an equality of parts, admitting neither of posterior and
anterior extremities, nor of right and left, nor of above and below,
in a structural sense. This animal also presents a seeming anomaly in
the mode of formation of the young tentacles, which always make their
appearance at the posterior extremity of the longitudinal axis, the
new ones being placed behind the older ones, instead of alternating
with them as in other Actiniæ.
_Bicidium_. (_Bicidium parasiticum_ AG.)
[Illustration: Fig. 14. Bicidium parasiticum; natural size.]
The Bicidium (Fig. 14), our parasitic Actinia, is to be sought for in
the mouth-folds of the Cyanea, our common large red Jelly-fish. In any
moderate-sized specimen of the latter from twelve to eighteen inches
in diameter, we shall be sure to find one or more of these parasites,
hidden away among the numerous folds of the mouth. The body is long
and tapering, having an aperture in the extremity, the whole animal
being like an elongated cone, strongly ribbed from apex to base. At
the base, viz. at the month end, are a few short, stout tentacles.
This Actinia is covered with innumerable little transverse wrinkles
(see Fig. 14), by means of which it fastens itself securely among the
fluted membranes around the mouth of the Jelly-fish. It will live a
considerable time in confinement, attaching itself, for its whole
length, to the vessel in which it is kept, and clinging quite firmly
if any attempt is made to remove it. The general color of the body is
violet or a brownish red, though the wrinkles give it a somewhat
mottled appearance. _Halcampa_. (_Halcampa albida_ AG.)
Strange to say, the Actiniæ, which live in the mud, are among the most
beautifully colored of these animals. They frequently prepare their
home with some care, lining their hole by means of the same secretions
which give their slimy surface to our common Actiniæ, and thus forming
a sort of tube, into which they retire when alarmed. But if
undisturbed, they may be seen at the open door of their house with
their many colored disk and mottled tentacles extending beyond the
aperture, and their mouth wide open, waiting for what the tide may
bring them. By the play of their tentacles, they can always produce a
current of water about the mouth, by means of which food passes into
the stomach. We have said, that these animals are very brightly
colored, but the little Halcampa (Fig. 15), belonging to our coast, is
not one of the brilliant ones. It is, on the contrary, a small,
insignificant Actinia, resembling a worm, as it burrows its way
through the sand. It is of a pale yellowish color, with whitish warts
on the surface.
[Illustration: Fig. 15. Halcampa albida; natural size.]
* * * * *
MADREPORIANS.
_Astrangia_. (_Astrangia Danæ_ AG.)
In Figure 16, we have the only species of coral growing so far north
as our latitude. Indeed, it hardly belongs in this volume, since we
have limited ourselves to the Radiates of Massachusetts Bay,--its
northernmost boundary being somewhat to the south of Massachusetts
Bay, about the shores of Long Island, and on the islands of Martha's
Vineyard Sound. But we introduce it here, though it is not included
under our title, because any account of the Radiates, from which so
important a group as that of the corals was excluded, would be very
incomplete.
[Illustration: Fig. 16. Astrangia colony; natural size.]
[Illustration: Fig. 17. Magnified individuals of an Astrangia
community in different stages of expansion.]
This pretty coral of our Northern waters is no reef-builder, and does
not extend farther south than the shores of North Carolina. It usually
establishes itself upon broken angular bits of rock, lying in
sheltered creeks and inlets, where the violent action of the open sea
is not felt. The presence of one of these little communities on a rock
may first be detected by what seems like a delicate white film over
the surface. This film is, however, broken up by a number of hard
calcareous deposits in very regular form (Fig. 20), circular in
outline, but divided by numerous partitions running from the outer
wall to the centre of every such circle, where they unite at a little
white spot formed by the mouth or oral opening. These circles
represent, and indeed are themselves the distinct individuals (Fig.
17) composing the community, and they look not unlike the star-shaped
pits on a coral head, formed by Astræans. Unlike the massive compact
kinds of coral, however, the individuals multiply by budding from the
base chiefly, never rising one above the other, but spreading over the
surface on which they have established themselves, a few additional
individuals arising between the older ones. In consequence of this
mode of growth, such a community, when it has attained any size, forms
a little white mound on the rock, higher in the centre, where the
older members have attained their whole height and solidity, and
thinning out toward the margin, where the younger ones may be just
beginning life, and hardly rise above the surface of the rock. These
communities rarely grow to be more than two or three inches in
diameter, and about quarter of an inch in height at the centre where
the individuals have reached their maximum size. When the animals are
fully expanded (Fig. 18), with all their tentacles spread, the surface
of every such mound becomes covered with downy white fringes, and what
seemed before a hard, calcareous mass upon the rock, changes to a soft
fleecy tuft, waving gently to and fro in the water. The tentacles are
thickly covered with small wart-like appendages, which, on
examination, prove to be clusters of lasso-cells, the terminal cluster
of the tentacle being quite prominent. These lasso-cells are very
formidable weapons, judging both from their appearance when magnified
(Fig. 19), and from the terrible effect of their bristling lash upon
any small crustacean, or worm, that may be so unfortunate as to come
within its reach.
[Illustration: Fig. 18. Single individual of Astrangia, fully
expanded.]
[Illustration: Fig. 19. Magnified lasso-cell of Astrangia.]
The description of the internal arrangement of parts in the Actinia
applies in every particular to these corals, with the exception of the
hard deposit in the lower part of the body. As in all the Polyps,
radiating partitions divide the main cavity of the body into distinct
separate chambers, and the tentacles increasing by multiples of six,
numbering six in the first set, six in the second, and twelve in the
third, are hollow, and open into the chambers. But the feature which
distinguishes them from the soft Actiniæ, and unites them with the
corals, requires a somewhat more accurate description. In each
individual, a hard deposit is formed (Fig. 20), beginning at the base
of every chamber, and rising from its floor to about one fifth the
height of the animal at its greatest extension. This lime deposit does
not, however, fill the chamber for its whole width, but rises as a
thin wall in its centre. (See Figs. 13, 17.) Thus between all the soft
partitions, in the middle of the chambers which separate them, low
limestone walls are gradually built up, uniting in a solid column in
the centre. These walls run parallel with the soft partitions,
although they do not rise to the same height, and they form the
radiating lines like stiff lamellæ, so conspicuous when all the soft
parts of the body are drawn in. The mouth of the Astrangia is oval,
and the partitions spread in a fan-shaped way, being somewhat shorter
at one side of the animal than on the other. The partitions extend
beyond the solid wall which unites them at the periphery, in
consequence of which, this wall is marked by faint vertical ribs.
[Illustration: Fig. 20. Limestone parts of an individual of
Astrangia; magnified.]
* * * * *
HALCYONOIDS.
_Halcyonium_. (_Halcyonium carneum_ AG.)
[Illustration: Fig. 21. Single individual of Halcyonium seen from
above; magnified.]