546 



A. A. W. HUBRECHT. 



anteriorly into the ' chorda-entoblast ' without any strict 

 boundary; all this together represents the material from which 

 the notochord will originate. But only w^hen the chorda- 

 entoblast and the intercalated ' KopfFortsatz ' (intercalated in 

 the hypoblast) have again become pinched off — only then the 

 definite notochord has originated. It is only the chorda- 

 entoblast at the cranial extremity and the gastrula ridge con- 

 tribution at the caudal extremity which^ as follows from this 

 description^ is directly converted into notochord. By further 

 differentiations in gastrula ridge and terminal knob the noto- 

 chord extends further backwards ; by further processes of 

 growth in the split-ofF chorda-entoblast it extends further 

 forwards.^^ 



The points of comparison between shrew and sheep will be 

 self-evident for whomsoever compares certain figures from 

 Bonnet's earlier paper {' Arch. f. Auat. u. Physiol./ 188-ij Anat. 

 Abth., pis. ix — xi) with those here given for the shrew/ more 

 especially — 



Bonnet's fig. 30 



,, „ 31, 32 



>j jj 29 



» 5> 28 



j> )i ^' 



„ » 53,54 



„ „ 57, 58 



» 59,60 



Finally I may draw attention to a fact which I am inclined 

 to attach importance to^ viz. that Bonnet describes and figures 

 in the anterior portion of the sheep's protochordal plate 

 numerous downward proliferations of this hypoblastic tissue, 



1 I hardly tliink Bonnet is justified in expressing doubt (p. 66, 1. c., 1889) 

 as to whether the median, anterior thickening of the hypobhist, noticed in 

 early stages in front of the KopfTortsatz, stands in any relation to the forma- 

 tion of the notochord. I must acknowledge that I cannot succeed in 

 connecting this statement with Bonnet's description of his " chorda-ento- 

 blast," which somewhat later occupies the same position (our protochordal 

 plate), and which would naturally be looked upon as a further thickening of 

 the region already similarly recognisable in the earlier stages. 



