ox THE PROCESS OF GASTRULATION IX CHELONIA. 269 



done in taking ont cliick-embryos. At tliat time, we used to find 

 Tri onyx embryos vaulted dorsally, just as Will describes in the 

 ({notation given above. Since adopting the method given in the 

 foregoing article of preserving embryos stretched in tlieir natural con- 

 dition, I have never found the shields vaulted in this manner at any 

 stage : they were always on a level with tlie rest of the blastoderm. 



7. In a note entitled " On Mcsoblast Formation in Gecko," 

 (Anat. A)iz.) No. 12 u. 13, 1893), 1 ventured to criticize Will's views 

 on the mesoblast formation of Reptiles. Will replies to my criticism 

 in the postscript to his second article, and :iIso in a note " Zur Frage 

 nach der Entstehung des gastralen Mesoderms bei Reptilien "' in the 

 Anafoinisclicr Anzeiijcr Xo. 20, 1803, wliich has just come to my hand. 

 I must refer the i-eader to Will's original pa])ers as well as to the above 

 note for his views. Suffice it to say here that AYill considers the 

 gastral mesoblast to be formed by a fold which arises in the outer wall 

 of the archenteron and grows towards the median line, thus cutting 

 otf tlie dorsal portion of the archenteron from its lower main portion. 

 The wall of the small dorsal portion thus cut otf is said to become the 

 mesoblast. This is put forth in (^p[)osition to tlie N'iew which was first 

 pro])oniided l)y Hertwig and which appears true to me, viz : that the 

 mesoblast is formed from two diverticula of the archenteron arising 

 directly on each side of the chorda. 



Will considers that Fig. 23 of my Contrib. III. which shows a. 

 distinct diverticulum on each side of the chorda can not be held to 

 prove the " Divei-tikelbildung " as it comes from an old embryo which 

 has the chorda already cut otf in the middle dorsal region. In his own 

 words* : '" Hier sielit man thatsachlich rechts und links neben der 

 Chorda ein kurzes Divertikel, von dem die solide Mesoblastmasse 

 ausgeht, jedoch lässt sich an einem solchen i^ild aus dem Ende des 



* The note above referred to. Anat. Anz. No. 20. p. 681. 



