98 



THE ECHINODERMATA. 



^98. 



§ 98. 



The few obsei'vations hitherto made upon the embryology of the Echino- 

 dorms belong solely to the Asteroidae. Here, the vitellus undergoes the 

 uflual segmentation, and then is changed into a long, cylindrical, infusorial 

 embryo, covered with cilia. 



A tew 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- 

 inof cavity (Brutholile). 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 Sarx (JViez- 

 mann's Arch. 1837, I. p. 404, IS-ii, I. p. 169, Taf. 

 VI. fig. i-22) were made upon Ec/iinaster san- 

 guinolentus, and Asteracaiithion MilUeri. 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 Müller 

 and Troschel (Syst. d. Ästenden, p. 13-1), 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. 182S, 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 {fViegmann^s Arch. 1844. I. p. 176) 

 that the animal which he formerly called Bipin- 

 naria asterigera (Beskrivelser, &c., p. 37, Tab. 

 XV. fig. 40) is probably only a developing As- 

 teroid endowed with a great swimming ajipara- 

 tus, deserves to be considered. The remark of 

 DalyeU {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. 



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. So. 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 i)Mrticular 



appendage, which is very complicated, and provided 

 with numerous oars, — an appendage which is sub- 

 sequently detacliea, but which continues then to 

 execute natatory movements. There were, per- 

 haps, sunilar appendages detached from young 

 Asteroids that Mailer and ffagner found at 

 Helgoland, and which they have described and 

 fitfured under the name of Actinotrocha branch- 

 lata; see Miiller^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 I'Acad. des Sc. de St. 

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

 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. Diifossi 

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

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

 Echinus esculentus, the development of these 

 infusoria-like embryos. They gradually became 

 pyriform, and acquired a peduncle at theii* 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 Mül- 

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

 p. 160) under the name of Pliiteus 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 supiiorted by a 

 frame composed of ten diverging, calcareous pro» 

 longations, resembling a painter's easel.* 



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

 368, Taf. XVI.). 



Peters has found that the fine whitish line de- 

 scribed by Grabe 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 



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 the Echino 

 derms has been much and successfully studied of 

 late, and chiefly by Müller, wlio, 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 embry- 

 ology. The writings of Ai;assiz and others fur- 

 nish also many details, but in any account I may 

 give I shall depend mainly on the first-mentioned 

 authority. 



