m 



THE KCHINODERMATA. 



§98. 



§98. 



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

 dcrms 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 (Bruthuhle). It then begins to be flattened laterally, and 

 upon one of those lateral surfaces, ray-like tentacles appear, while the 

 niar<fin of the body forms live angles, ujioii 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. ''* 



t These interestinp; observatiniH of Sfjr/t {JViei;- 

 mann's Arch. 1837, I. p. 4U1, 1841, I. p. IGJ, T;if. 

 VI. fig. 4—22) were inatle upon JCrJiinaxter san- 

 guinolentus, ami Asteracant/iion Mulleri. Hi; 

 lias also observed that dariiii; the development, 

 the point of attachment is ;;raJually changed, until 

 it reaches the back ; thus suppurting ths view that 

 the madreporal jilate is the relic uf this last, which, 

 in Comatula, has been well comjiared by MuUer 

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

 button, sinc2 from it the young individuals are 

 attached by a pedicle, as Thomson has shown 

 upon (formerly) Pentacrinas Europaeus ; S3e 

 Zeitsch. f. die Organisch. I'liysik. 182S, p. 55, and 

 the Edinb. new I'hilos. Jour. 1836, p. 236, or Fro- 

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

 tion of Sws {If'ie^rmanii's Arch. 1844. I. p. 176) 

 that the animal which he formerly called Bipin- 

 naria asterii^cra (Baskrivelser, &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 {Frorie/i's n.'ue Not. N .). 331, p. 2) that 

 the young of Holothiiria are of the size of bar- 

 ley-corns, anil resemble white maggots, is not one 

 that affords us any data upon the development of 

 these animals. Tliere remains, therefore, a vast 

 field open to observers concerning the development 

 of the Echinoderms. 



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

 numerous data on the development oi Echinaster. 

 It appears, moreover, that all tlie Asteroidae are 

 not developed after this type ; for, Koren and 

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

 PI. VII. flg. 7-0) have shown that Bipinnaria 

 axterisie.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 apjiendage which is sub- 

 sequently detacliea, but which ontinues then to 

 e.Kecute natatory movements. There were, per- 

 haps, smillar aiipendages detached from young 

 Asteroids that MuUer and IVa^ner fjund at 

 Helgoland, and which they liave described and 

 figured under the name of Actinotrocha brancli- 

 iata ; see Muller^s Arch. 1S46, p. 101, T.if. V. 

 fig. 1, 2, and 1847, p. 202, Taf. IS., fig. 1-S. 



Various naturalists have noticed interesting facts 

 on the development of the Echinidae in endeavor- 

 ing to produce artificial fecundation. In tlie 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. XXXI.X. 

 p. 36), the eggs of Echhius esculentus, and liii- 

 dus, thus facundated, were transformed, after a 

 complete segmentation of the vitelluj, into a round, 

 infusoria-like body, covered with cilia. Dufossi 

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

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

 Echinus esculentus, the development of tliese 

 infusoria-like embryos. They gradually became 

 pyriforin, 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 Miil- 

 ler (Arch. 1S4Q, p. lOS, Taf. VI. flg. 2, 3, and 1847, 

 p. 160) under the name of Platens paradoxus, 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 supjiorted by a 

 frame composed of ten diverging, calcareous pro- 

 longations, resembling a painter's easel.* 



332, Taf. rv. fig. A— I^), and Krohn (Iljid. 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, wliicli move along by the action of the cilia 

 vith wliich it is lined. Connecting with this ovi- 

 duct are botryoidal appendages, situated on the 

 hitostine, 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 Uirough two brownish tubes, which open 

 externally, and whose internal extremity is not 

 closed, as has hitherto been supposed, but opeua 



into the general cavity of the body. These tubes, 

 or oviducts, have been regarded hitherto as respir- 

 atory or secreting organs. Krohn''s observations 

 confirm those of Peters on this point. — Ed. 



* [§98, note 1.] The development of th 3 Echino. 

 derms has been much and successfully studied of 

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

 cessive memoirs (see loo. cit.), has changed the 

 zoological face of this class, beside making himself 

 the great authority on all that relates to its embry- 

 ology. The writings of A^assiz and others fur- 

 nish also many details, but in any account I may 

 give I shall depend mainly on the first-mentioned 

 authority. 



