422 



gins, and it is a question how far it has been used up in forming a 

 secretion. 



A hypochordal cuticle, described in certain Amphibia by Field, 

 Bergfeldt and Reinhardt, but not by Stöhr, is absent in the sltate. 

 In none of the Ichthyopsidan embryos that I have examined have I 

 seen anything more than the clear ectoplasm characteristic of the 

 free borders of cells. 



In damaged embryos the hypochordal rudiment may break away 

 from the hypoblast, but it never parts from the notochord. 



Phylogeny of the Ichthyopsidan Hypochord. 



Very meagre are the facts which can be fastened upon for guid- 

 ance. And our knowledge of the phylogeny of the notochord, with 

 which the hypochord has such intimate relations, is deficient enough. 

 Definite knowledge of the fate of the lateral parts of the chorda- 

 hypoblast in other groups of the Chordata would have been a great 

 help; but it is not to be obtained. 



Take first the case of Amphioxus, in which the hypochord is ab- 

 sent. Hatschek (14) stated that the formation of the notochord did 

 not involve the whole of the chorda-hypoblast, and that some cells 

 remained in the roof of the gut. Lw^off (26), on the contrary, asser- 

 ted that the whole of it was devoted to the notochord, and that the 

 gut roof was formed by hypoblast primitively lateral to the meso- 

 blastic diverticula. But his belief must be mentioned that the noto- 

 chord, with the possible exception of its anterior end, arose from an 

 ectoblastogenetic rudiment, its connection with the hypoblast during 

 development being secondarily assumed. 



In the case of the Amniota, I cannot admit that the hypochord 

 is present in their embryos; and in the succeeding section of this paper the 

 position is taken up that what has been described in them as the 

 hypochord is really homologous with the epibranchial groove of Am- 

 phioxus. What is the fate, then, of the lateral parts of the chorda- 

 hypoblast? A number of papers contain the statement that the hypo- 

 blast passes beneath both mesoblastic rudiments and chorda-hypo- 

 blast and occludes them from the lumen of the gut; yet the pertaining 

 observations have not been made with the hypochord in mind. If 

 hypochordal cells are actually non-apparent, this may be because the 

 whole of the chorda-hypoblast is devoted to the notochord, or because 

 the cells have disappeared entirely from the life-history, or because 

 they disappear early in development and have escaped notice. These 

 considerations apply also to the case of Amphioxus. 



