364 Miscellaneous. 



nective perienteric tissue, in the parenchyma of which the in- 

 ternal organs are lodged and fixed. Hence M. Grenacher concludes 

 that it is necessary to separate Oordius, more than is usually done, 

 both from Merm'is and from the true Nematodes, at the same time 

 approximating Mermis to the latter. — Ze/fec/ir. fiw ivlss. Zoologie, 

 xviii. p. 322 ; Blhl Univ. August 15, 1869, JSidl. ScL pp. 308- 

 311. 



On tlie Development of Pelohates fuscus, Warjl. 

 By C. VAN Bambeke. 



The author treats of a subject which has not hitherto been inves- 

 tigated — the embryogeny of Pelohates fuscus. His history of its 

 development commences with the ovarian egg, and closes at the 

 period when the internal branchia3 replace the external branchite — 

 that is to say, when the principal organs are sketched out. He first 

 of all describes the process which he has followed in making his 

 preparations. The object is to obtain sections sufficiently delicate 

 for microscopic examination by transmitted light, this method being 

 the only one which leads to positive results in the anatomical inves- 

 tigation of the various phases of embryonic development. For fur- 

 ther details the reader must refer to the memoir. 



The ovum is described, with the appearance which it presents in 

 the ovary. The deposition of the secondary vitellus in the proto- 

 plasm of the primordial ovum takes place uniformly round the ger- 

 minal vesicle, and not in the form of a nucleus ; the germinal vesicle 

 is enclosed in a cavity closely approximated to the periphery of the 

 ovum, and has no external communication by a canal ; the rupture 

 of the germinal vesicle always precedes the quitting of the ovary by 

 the ovum ; and there is no true \'itelline membrane {Eizelhnembran 

 of Remak). These are the chief peculiarities presented by the ovum 

 before its extrusion. 



In the upper hemisphere of the fecundated ovum a clear solid 

 nucleus makes its appearance ; this becomes the starting-point of 

 the segmentation, which sometimes commences upon the \cry border 

 of the germinal pit {fovea germinativa of Schultze). The circlet of 

 folds {Faltenlcranz of the Germans) is very distinct in the ovum of 

 Pelohates during the first phases of segmentation. The division into 

 two spheres takes place in such a manner that the part still undi- 

 vided, instead of being central, occupies the iieriphery of the ovum, 

 and corresponds to the inferior pole. 



The formation of the primitive visceral cavity results from the 

 multiplication of the ceUs of the deeper layer of the dome which 

 covers the cavity of segmentation. In consequence of this cellular 

 prolification, the above-mentioned layer is incurved and covers the 

 clear hemisphere. As soon as the primitive visceral cavity has re- 

 placed the cavity of segmentation, the embryonal lamella) are dis- 

 tinct. Of these tliere are four, namely :■ — 



1. An external lamella (enveloping membrane). 



