510 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKEll. 



^equator. Owing to this rotation the now laterally placed 

 dorsal half is turned outwards. This rotation is occasioned 

 by the formation of a second cavity which extends along the 

 dorsal half. By this means the centre of gravity of the 

 ovum is displaced, and the rotation is a necessary consequence. 

 This second cavity (N, fig. 401) was recognized by Rusconi * 

 Golubewf has by historical inquiry discovered some erroneous 

 references in the nomenclature of the two cavities, and has 

 shown that the cavity of Baer is to be regarded as elliptic, 

 but that of Rusconi as semilunar. 



Remak:}: was of opinion, on theoretical grounds, that the 

 cavity of Rusconi originates from the furrow of the same 

 name by an inversion. He considered that the germ of the 

 Bird is composed of three cell layers or lamina?. The most 

 superficial or most external he named the corneal or sexisorial 

 lamina (Hornblatt oder sensorielles Blatt) ; the second, the 

 middle or motor, or motor-germinal lamina (mittleres oder 

 motorisches, auch motorisch gerrninatives Blatt), and the third 

 the intestinal glandular lamina (Darmdriisenblatt). That the 

 Avian germ is laminar, and curves downwards, has been known 

 from the time of C. F. Wolf. Remak believed he could 

 establish the analogy between the Avian and the Batrachian 

 germ by the following observations. 



He sought the analogue of the sensory and motor laminae in 

 the cover or roof of the cleavage cavity ; the analogue of the 

 gland-layer of the Bird, on the other hand, in the white area 

 at the inferior pole of the Batrachian ovum. The germ of the 

 Frog, he remarked, is certainly not laminar, and therefore 

 cannot curve inwards in the same manner as the Avian germ. 

 On the other hand, the lower surface of the spherical Batrachian 

 germ undergoes inversion, in order to become applied to the 

 motor laminse, which he himself, as above stated, believed to be 

 already completed at the inner surface of the mantle layer. 

 I have however shown that the Rusconian groove is produced 



* Mullens Archiv, 1836. 



t Hollett, Untersucihungen. Leipzig, 1870. 



Loc. cit. 



Loc. cit. 



