§ 98. 
98 THE ECHINODERMATA. 
§ 98. 
The few observations hitherto made upon the embryology of the Hchino- 
derms belong solely to the Asteroidae. Here, the vitellus undergoes the 
usual. segmentation, and then is changed into a long, cylindrical, infusorial 
embryo, covered with cilia. ; ; 
A few days after, four papillae are formed upon the anterior part of 
the body, and by these the embryo is attached to the walls of the incubat- 
ing cavity (Bruthdhle). It then begins to be flattened laterally, and 
upon one of these lateral surfaces, ray-like tentacles appear, while the 
margin of the body forms five angles, upon the extremity of each of which 
is a red pigment dot. Then the cilia upon its surface disappear, and the 
young individual, deprived of its papillae and set free, moves about by its 
ambulacra.© 
1 These interesting observations of Sars (Wieg- 
mann’s Arch. 1837, I. p. 404, 1844, I. p. 169, Taf. 
VI. fig. 4-22) were made upon Echinaster san- 
guinolentus, and Asteracanthion Miulleri. He 
has also observed that during the development, 
the point of attachment is gradually changed, until 
it reaches the back ; thus supporting the view that 
the madreporal plate is the relic of this last, which, 
in Comatula, has been well compared by Miller 
and Troschel (Syst. d. Asteriden, p. 184), to a 
button, since from it the young individuals are 
attached by a pedicle, as Thomson has shown 
upon (formerly) Pentacrinus: Europaeus; see 
Zeitsch. f. die Organisch. Physik. 1828, p. 55, and 
the Edinb. new Philos. Jour. 1836, p. 296, or Fro- 
riep’s neue Not. No. 1057, 1836, p.1. The asser- 
tion of Sars (Wiegmann’s Arch. 1844. I. p. 176) 
that the animal which he formerly called Bipin- 
maria asterigera (Beskrivelser, &c., p. 37, Tab. 
XV. fig. 40) is probably only a developing As- 
teroid endowed with a great swimming appara- 
tus, deserves to be considered. The remark of 
Dalyell (Froriep’s neue Not. No. 331, p. 2) that 
the young of Holothuria are of the size of bar- 
ley-corns, and resemble white maggots, is not one 
that affords us any data upon the development of 
these animals. There remains, therefore, a vast 
field open to observers concerning the development 
of the Echinoderms. i 
Sars (loc. cit. p. 47, Taf. VIII.) has furnished 
numerous data on the development of Echinaster. 
It appears, moreover, that all the Asteroidae are 
not developed after this type; for, Koren and 
Danielssen (Ann. d. Sc. Nat. VII. 1847, p. 347, 
Pl. VII. fig. 7-9) have shown that Bipinnaria 
asterigera first observed by Sars, is a young As- 
teroid which moves by means of a particular 
882, Taf. IV. fig. A—H), and Krohn (Ibid. 1850, p. 
368, Taf. XVI.). 
Peters has found that the fine whitish line de- 
scribed by Grube'as lying contiguous with the blood- 
vessel of the intestine is an oviduct, being filled with 
ova, which move along by the action of the cilia 
with which it is lined. Connecting with this ovi- 
duct are botryoidal appendages, situated on the 
intestine, and filled with eggs ; these are the ovaries. 
The eggs, when matured, escape into the general 
cavity of the body, and thence are transferred out~ 
wardly through two brownish tubes, which open 
externally, and whose internal extremity is not’ 
closed, as has hitherto been supposed, but opens 
appendage, which is very complicated, and provided 
with numerous oara,— an appendage which is sub- 
sequently detached, but which continues then to 
execute natatory movements. There were, per- 
haps, similar appendages detached from young 
Asteroids that Miller and Wagner found at 
Helgoland, and which they have described and 
figured under the name of Actinotrocha branch- 
tata; see Muiiller’s Arch. 1846, p. 101, Taf. V. 
fig. 1, 2, and 1847, p. 202, Taf. IX. fig. 1-6. 
Various naturalists have noticed interesting facts 
on the development of the Echinidae in endeavor- 
ing to produce artificial fecundation. In the first 
of these experiments, by Baer, in 1845 (Bull. de. 
la Classe physico-math. de PAcad. des Sc. de St. 
Petersburg, V. p. 234, Froriep’s neue Not. XX XIX. 
p. 36), the eggs of Echinus esculentus, and livi- 
dus, thus fecundated, were transformed, after a 
complete segmentation of the vitellus, into a round, 
infusoria-like body, covered with cilia, Dufossé 
and Derbés (Ann. d. Sc. Nat. VII. 1847, p. 44, and 
VIII. p. 80, Pl. V.) followed still further, with 
Echinus esculentus, the development of these 
infusoria-like embryos. They gradually became 
pyriform, and acquired a peduncle at their smaller 
anal extremity ; while at the larger, oral end, 'ten- 
tacles and several long calcareous spines were 
developed. At the same time the digestive canal 
was formed in the interior of the body. 
A small marine animal, first described by Mul- 
ler (Arch. 1846, p. 108, Taf. VI. fig. 2, 8, and 1847, 
p. 160) under the name of Pluteus paradowus, has 
been recently found by this same naturalist to be 
the young of an Ophiura. This animal swims by 
means of vibratile cilia, and' is supported by a 
frame composed of ten diverging, calcareous pro- 
longations, resembling a painter’s easel.* 
into the general cavity of the body. These tubes, 
or oviducts, have been regarded hitherto as respir- 
atory or secreting organs. Krolin’s observations 
confirm those of Peters on this point. — Ep. 
* [§ 98, note 1.] The development of the Echino- 
derms has been much and successfully studied of 
late, and chiefly by Muller, who, by several suc- 
cessive memoirs (see loc. cit.), has changed the 
zoological face of this class, beside making himself 
the great authority on all that relates to its evabry- 
ology. The writings of Agassiz and others fur- 
nish also many details, but in any account I may 
give I shall depend mainly on the first-mentioned 
authority. 
