ox THE PROCESS OF ÖASTRULATION IN CHELONTA. 2T1 



licrvoro-eheii." (/^/*?V) The first of these ohjections occnrred to me, 

 while writino- mv (^ontril). III. If one examines tlie cross-sections of 

 Amphioxns ns o-iven, for instance, in Hatschek's Taf. IX. (Sfiidioi ti. 

 Entiv. (J. Jiiipliio.rus. Arh. a. d. Zool. Inst, Wien. Bd. TV. See also 

 Hertwig's Lehrlnich fio-. 72), we shall find that the mesoblnst ])ouch 

 sprenfls ventrnlly :tnd laterally not from what «corresponds to the 

 npex of the earlier diverticulum, but from its outer or lateral wall. 

 The same thinü' takes place in Reptiles, Although I did not express 

 this distinctly, it was present in my mind, as a reference to the middle 

 of p. 41 (Contrib. III.) will show. These two objections on the part 

 of Will are, I think, fully answered by this consideration. 



Will again says : " Die Urdarmfalte würde bei der Mitsukuri'schen 

 Auffassung überhaupt belanglos für die Mesodermbildung und deshalb 

 unverständlich sein " (loc. cit. p. 681), I do not quite see the force 

 of this objection. A fold is ueeded to m.ark the outer limit <^f the 

 di\ erticulum,* and when tlie diverticulum is finally to be cut off from 

 the main portion of the archenteron, it takes place by this fold advan- 

 cino- towards the median chorda. I described this inw^ard moveiuent 

 of the fold! in my contrib. III. (pp. 42 and 4() ; also Figs. lG-17). 

 It is this last ])hase of tlie mesoblast formation which Will ein]>hasizes 

 above all others, and on which lie builds what he considers to be a new 

 theory of the mesoblast formation (I Art. p. 102). Even in his own 

 views tlie ]iart of the mesoblast which is formed by " Septenbildung " 

 is only a smidl ])roximal ])ortion near the chorda, for the part wgr in 

 his fig. 1 B. C. D. (Anat. Anz. No. 20, 1893) is according to himself 

 not formed by " Septenbildung" but proliferated from the archenteric 



* In a sent(,'nce siuiilar to the above, in my note " On the Mesoljlast Formation in Gecko " 

 (Auat. Anz. Xo. 12-13, 1893) the word "mark" is by a most unfortunate oversight in proof- 

 reading misprinted " snack " — a mistake which makes my sentence Avell nigh incomprehensible. 



t I admit that I used then the expression " gut-hypoblast " — instend of the word " fold " 

 whicli I ought to have adopted. But a reference to figs. 16-17 will show that a« a, matter of 

 fact I had observed a fold. 



