TO THE EMBRYOLOGY OF AMPHIBIA. 35 



appearance some degrees below the equator, although there are 

 variations in this distance from the equator according to different 

 species and to different individuals of the same species. In Rha- 

 cophorus, it is generally at 10°-20° below the equator, although 

 in rare cases it may go up to 5° or down to 25°. In Bufo, it 

 is at about 28°-30°. The same fact may be made out from the 

 papers of Morgan and Tsuda ('95Ô), Assheton ('94a), Kopsch 

 ('oo), Eycleshymer ('95a, '98), and other authors. 



2). The completion of the blastopore lip in a circle, or in 

 other words the first appearance of the ventral lip may also vary : 

 it takes place generally at about the time when the dorsal lip 

 has grown down to about 50° below the equator in Rhacophorus, 

 and to about 60° in Rana and Bufo. 



3). The blastopore remains circular throughout its existence, 

 since the dorsal and the ventral, as well as the lateral lips close 

 in towards the center of the blastopore area equally from all 

 around. Owing to the rotation of the egg as a whole, it looks, 

 however, in later stages as if there were a difference of growth in 

 different parts. That the entire rim of the blastopore takes part 

 in its closure has already been recognized directly or indirectly 

 by Schulze ÇS&b.c), Assheton ('94a), Eycleshymer ('95«, '98), 

 and Kopsch ('oo), in opposition to the views of Pflüger ('83), 

 Eoux ('88a), Morgan ('93, '97) et al. The former authors, 

 however, seem to me to be of the opinion that there is a 

 certain difference between the growing ratios of the dorsal and 

 the ventral lips of a blastopore. And moreover, the fact that 

 the actual final closing point of the blastopore is the former yolk 

 pole (the center of the blastopore area), of the egg, has not yet 

 been maintained by any previous writer. This is probably due 

 to the circumstance that the methods hitherto employed are not 



