No. 2.] EARLY DEVELOPMENT OF AMBLYSTOMA. 367 



and Jordan ('93) in the Newt, state that it first appears at the 

 vegetative pole. 



I have examined a large number of eggs at this stage to 

 determine what relation this line bears to the more deeply pig- 

 mented area of the superior hemisphere to which I have 

 already referred. In all eggs where the differences are suffi- 

 ciently marked to admit of orientation, the irregular line lies 

 beneath the darker portion and is parallel with its more 

 sharply defined border. It will be recalled that the deeply 

 pigmented area is the area in which cell-division has become 

 much accelerated (PI. XVIII, Figs. 21, 22). 



Concerning this peculiar distribution of pigment there are 

 but few references in the literature. Roux ('83) observed cer- 

 tain differences in the Frog as expressed in the following 

 words: "Von der Gastrula ist es bekannt, dass schon bald 

 nach Beginn ihrer Bildung die Ruckenseite des Blastoporus an 

 dunklerer Farbung kenntlich ist, womit zugleich der Punkt 

 bezeichnet ist, an dem die Ruckenfurche sich zu entwickeln 

 beginnt." 



Hertwig ("82) found in Triton "dass der Dotterpfropf keinen 

 gleichmassigen Anblick darbietet, insofern eine Halfte ganz 

 pigmentfrei ist und weissgelb aussieht, die andere aber ein 

 wenig braunlich pigmentirt ist. Ferner ist auch der an die 

 weissgelbe Halfte des Dotterpfropfes angrenzende Theil des 

 Eies viel schwarzer pigmentirt als die Umgebung der anderen 

 Halfte. Nach diesen Verschiedenheiten kann man sich iiber 

 dorsal und ventral an der Kugeloberflache orientieren, da die 

 unpigmentirte Partie des Dotterpfropfes der Riickenflache des 

 Embryo zugekehrt ist." 



Houssay ('90) observed the extension of the pigment to be 

 "plus rapide sur le cote qui deviendra le dos de I'embryon." 



While the point in question is not referred to, it is evident 

 that the observations on the Frog, Triton, and Axolotl, as well 

 as those of Kolliker (-79), on the Chick, and Lwoff ('92), on 

 Amphioxus, accord perfectly with what I have found in 

 Amblystoma. Morgan and Tsuda ('94) hold, however, that 

 " in Rana the blastopore appears on the less pigmented and 

 further developed side of the egg." 



