M. Ussow's Zoologico-Einhryological Investigations. 99 



or less detailed and accurate memoirs, which are chiefly de- 

 voted to the embryology of the Decapoda. 



As early as the year 1841 \'an Beneden ])ublished his inves- 

 tigations on Sepiola RondeUtii* . In 1844 KoUikerf enriched 

 science with his well-known memoir on the development of 

 various species of Decapod and Octopod Cephalopoda. Almost 

 a quarter of century later (1867) E. Metschnikoff :t made known 

 his investigations on Sepioki] and la.st year (1873) Ray Lan- 

 kester published a short communication § on the development 

 oi LoUgo. It seems scarcely necessary to enumerate the obser- 

 vations of Cuvier||, DugJis^, and Delle Chiaje** relating to 

 this subject, as in most cases they contain very unsatisfactory 

 and erroneous ft statements as to the embryonal process. As 

 it is impossible for me in this short summary to submit the 

 results obtained by Van Beneden and Kolliker to criticism, 

 and as in the following report upon my investigations I indi- 

 cate the most important eiTors of those savants, I shall devote 

 a moment only to the most accurate of all these memoirs, that 

 of E. Metschnikoff. 



We may regard as one of the greatest merits of the above- 

 mentioned important memoir, which only relates to one 

 species of Cephalopod, tlic first description of two germ- 

 lamella?, and the more or less exact indication of the part 

 they take in the subsequent formation of the different organs. 

 Studying the development of Sepiola and the mode of forma- 

 tion of the central nervous system, the intestinal canal, and the 

 central organs of circulation solely in living embryos U, with- 

 out the aid of dissected preparations, must necessarily have 

 caused Metschnikoff to miss many important facts, even with 

 regard to the species investigated by him. As, moreover, 

 from want of material, he was unable to trace the development 

 of the ova, and especially their process of segmentation, this 



* " Rech. sur rembryoL des S^pioles," in M^m. de I'Acad. de Bnix. xiv. 



t Loc. cit. 



X Historv of the embryological development of Sepiola (in Russian), 

 18G7. See" Arch, fiir Naturg. 1868, Bd. u. p. 130, and Arch, des Sci. Phvs. 

 et Nat. XXX. (1807) p. 186. The following citations apply to the complete 

 Russian work. 



§ Ann. .t Mag. Nat. Hist. 1873, no. 62, p. 81. 



II Ann. du Mus. 1832, i. p. 153. 



^ Ann. des Sci. Nat. viii. p. 107, 1837. 



** Memorie, 2nd edit. p. 30, 1829; Notom. degli anim. invertebr. 1841, 

 i. p. 83, pi. xxix. figs. 4, 5. 



tt KoUiker, /.o. pp. 110, 111. 



XX At least, in his memoir, Metschnikoff nowhere mentions that he 

 studied sections, without which it is impossible to trace the formation of 

 the intestino-fibrous layer, and to form a clear idea of the development of 

 some organs. 



7* 



