640 A. A. W. HUBREOHT. 



lines remains unnoticed. From this I have extracted such 

 points as seem to have special bearing on the subject here 

 treated, either as directly confirming or as in apparent contra- 

 diction to what has above been described for Sorex. 



1. The Protochordal Plate of Rabbit and Cavia. 



Carius' dissertation (p. 26) purposely refrains from deciding 

 whether in the rabbit there might not possibly be a participa- 

 tion of the entoblast towards the formation of anterior portions 

 of the notochord. A comparison of his fig. 8 with our figs. 

 44, 67, 70, and 71 undoubtedly suggests the presumption of 

 their homology, i. e. of the presence also in the rabbit of a 

 distinct hypoblastic protochordal plate which certainly is less 

 distinct at the outset in the rabbit than we have found 

 it in the shrew. In that case we shall also be allowed to 

 institute more direct comparisons between the figures which 

 he gives of the changes in the blind fore-gut with what 

 is found in the shrew, but has not been entered upon in this 

 paper. 



Concerning Cavia Carius is much more emphatic in denying 

 any participation of hypoblast in the formation of the noto- 

 chord. Here, too, a renewed comparison with what the 

 shrew has taught us will allow us to decide whether the proto- 

 chordal plate is perhaps so much reduced that it most 

 naturally escapes detection, or whether it is wholly absent, 

 the protochordal wedge supplying the whole of the notochord. 

 At all events, the extreme inversion of the layers, as we 

 find it in Cavia, must necessarily induce us not to look 

 upon Cavia as a fit representative oi the normal mammalian 

 development. 



Keibel's publication (17) concerning the formation of the 

 notochord is posterior to that of Carius, and on p. 27 of the 

 reprint of his article he holds himself justified to exclude 

 for the rabbit any participation of the hypoblast towards the 

 formation of the notochord. He recognises that at the fore- 

 most extremity the decision in the sense he advocates is 



