274 



K. MITSUKURI. 



simply lit such u figure as Fig. la of the foregoing article, we might 

 naturally come to the conclusion that the invagination ca\'ity gives 

 rise only to the gastral mesoblast and the chorda, and has nothing to do 

 with the formation of the definitive alimentary tract. But we should 

 always remember îi fact which I hope to have proved conclusively in 

 the foregcji ng article that t he 1 j o 1 1 o m o f t h e i n v a g i n a t i o n c a v i t y 

 has been removed. When the bottom is still present, we may 



Fig. c. 



Diagrauiiiiatic CruBS-section of the 

 Invagination-Canity ill Chelonia. ^^S- ^■ 



Diagrammatic Cross-section of the 

 Archenteron of Amphioxus. {■■iftcj- 

 Göttc, from Born. Ergehu. d. Anat. u. 

 Entw. I Bd. p. 49a.) 



represent the cross-section of the invagination cavity as in Fig. C. The 

 dark portion is the part that is removed. AVhen we comjjare it witli 

 a homologous section of Amphioxus (Fig, D.) we are struck with their 

 similarity and I think, we are justified in concluding that the invagi- 

 nation cavity of the reptilian ovum is homologous with the archenteron 

 of Amphioxus, and has potentially present in it not only the chorda 

 and the mesoblast but also the definitive alimentary tract. The re- 

 m<jval of the bottom, or that part whicli represents the definitive hypo- 

 blast, must in any case be regarded as a secondary process, and can 

 not stand in the way of homologizing the two structures. These 

 considerations, together with the reasons which I have brought out in 

 the foreofoini»' article, incline me more t(jwards those views which \ have 

 set forth in tlie preceding pages than to those of Keibel and of Fwotf. 



