98 



THE ECHINODERMATA. 



^98. 



§98. 



The few observations hitherto made upon the embryology of the Echino- 

 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 (Bruthohle). 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 {Wie,!;- 

 mann's Arch. 1837, I. p. 404, 1844, I. p. 169, Taf. 

 VI. fig. 4-22) were made upon Ec/iina.iter snn- 

 giiinolentus, and Asteracanthion MuUeri. lie 

 has also observed tiiat during the development, 

 the point of attachment is gradually changed, until 

 it reaches the back ; thvis supporting the view that 

 the madreporal plate is the relic of this last, which, 

 in Comatula, has been well compared by Miiller 

 and Trosckel (Syst. d. Asteriden, p. 134), to a 

 button, since from it the young individuals are 

 attached by a pedicle, as Thomson has shown 

 upon (formei'ly) Pentacrinus Europaetis ; see 

 Zeitsch. f. die Orgauisch. Physik. 1S28, p. 5-5, and 

 the Edinb. new I'liilos. .Tour. 1836, p. 296, or Fro- 

 riep''s neue Not. No. 1057, 1836, p. 1. The asser- 

 tion of Sars (^IFie^mann^s Arch. 1844. I. p. 176) 

 that the animal which he formerly called Bipin- 

 iiaria asteri^era (Beskrivelser, &c., p. 37, Tab. 

 XV. fig. 40) is i^robably only a developing As- 

 teroid cndov/ed with a great swimming appara- 

 tus, deserves to be considered. The remark of 

 Daly ell {Froriep^s nene Not. No. 331, p. 2) that 

 the young of Holothuria are of the size of bar- 

 ley-corns, and resemble wliite maggots, is not one 

 tliat aflfords us any data upon the development of 

 these animals. There remains, therefore, a vast 

 field open to observers concernhig the development 

 of the Echinoderms. 



Sars (loc. cit. p. 47, Taf. VIII.) has furnished 

 tmmerous data on the development of Echinaster. 

 It appears, moreover, that all the Asteroidae are 

 not developed after this type ; for, Korea and 

 Danielssen (Ann. d. Sc. Nat. VII. 1847, p. 347, 

 PI. VII. fig. 7-9) have shown that Bipinnaria 

 asterigp.ra first observed by Sars, is a young As- 

 teroid which moves by means of a particular 



appendage, which is very complicated, and provided 

 with numerous oars, — an appendage which is sub- 

 sequently detachea, but which continues then to 

 execute natatory movements. There were, per- 

 haps, similar appendages detached from young 

 Asteroids that Mailer and Wagner found at 

 Helgoland, and which they have described and 

 figured under the name of Actinotrocha branch- 

 iata ; see MuUer''s Arch. 1846, p. 101, Taf. \. 

 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 I'Acad. des Sc. de St. 

 Petersburg, V. p. 234, Froriep''s neue Not. XXXIX. 

 p. 3'6), the, eggs of Echinus esculentus^ and iivi- 

 dus, thus fecundated, were transformed, after a 

 complete segmentation of the vitellus, into a round, 

 infusoria-like body, covered with cilia. Dufossi 

 and Derbis (Ann. d. Sc. Nat. VII. 1847, p. 44, and 

 VIII. p. 80, PI. V.) foUowed still further, with 

 Echinus esculenttis, the development of these 

 infusoria-Uke 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 Mai- 

 ler (Arch. 1846, p. 108, Taf. VI. fig. 2, 3, and 1847, 

 p. 160) under the name of Pliiteus paradoxus, has 

 been recently foiuid by this same naturalist to be 

 the young of an Ophinra. 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.* 



382, Taf. TV. fig. A— II), and Krohn (Ibid. 1850, p. 

 368, Taf. XVI.). 



Peters has found that tlie 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 ciha 

 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 



into the general cavity of the body. These tubes, 

 or oviducts, have been regarded hitherto as respir- 

 atory or secreting organs. KroluVs observations 

 confirm those of Peters on this point. — Ed. 



* [ § 98, note 1.] The development of the Echino- 

 derms has been much and successfully studied of 

 late, and chiefly by Miiller, who, by several suc- 

 cessive memoh's (see loc. cit.), has changed the 

 zoological face of this class, beside making himself 

 the great authority on all that relates to its embry- 

 ology. Tlie 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. 



