14 



Except for the greater size of the vesicle fig. 26 of Willey ') 

 is whoUy comparable with the analogous stage figured by Yon 

 Kennel (fig. 56). Characteristic for the American species is only 

 the fact, that the invagination takes place in a very young stage. 



This phcnomenon, viz. the sinking of the embryonic area in 

 the trophic vesicle, again lias an analogon in Pohjijonlius^ viz. 

 the invagination of the „Rumpfkeim" in the „endolarva", as des- 

 cribed by Woltereck and Salensky. 



If one considers in this manner the development of the American 

 species as a modification of that of Peylpatopsis and Paraperipatiis 

 it is easily to be understood that the strand, connecting in American 

 species the „placenta" with the embryo, the „iimbilic cord" of 

 VoN Kennel, is attached dorsally at the cephalic end of the em- 

 bryo : the sanie is the case with the trophic vesicle in the older 

 stages of ParaperipatKs and of Peripatopsis Sedgwicki. 



In older embryos Von Kennel found lying against the inner 

 surface of his „uterine epithelium" another cell layer, which of 

 course he only could consider as ectodermal and which he des- 

 cribes as „amnion". Sclater rejects this interpretation, but could 

 not give another explanation of this layer. By comparing analo- 

 gous stages of Peripatopsis it does not seem doubtful, that this 

 problematic layer is entodermal and in all points comparable with 

 the entodermic cell layer of the trophic vesicle of Peripatopsis. 

 It is true that this layer in Peripatiis does not arise by a typical 

 invagination as in Peripatopsis. This however is to bc explained 

 by the small size, to which the embryonic area in Peripatiis has 

 been reduced, and which is the causc, that the blastoporus is no more 

 recognizable. About the manner in which the here mentioned 

 cell layer takes his origin, VoN Kennel's results were not conclu- 

 sive. It however certainly arises by a kind of delamination from 

 the embryonic area, and thus at the spot, whcre gastrulation can 

 bc expected. In this there is an analogy with the gastrulation of 

 Mammals and some figures of Yon Kennel show a remarkable 



1) l.c. (1898) 



