DEVELOPMENT OF SPELERPES BILINEATUS 233 



Amount of advance of dorsal lip 



An examination of the ventral views of the eggs shown in figs. 

 48-63, shows that aside from the shif tings of the blastopore, 

 the movement of the dorsal lip ventrally is much less than that 

 of the fcog. After their initial elongation, marks above the dor- 

 sal lip undergo comparatively little extension until after the 

 embryo begins to lengthen, while those ventral to the blastopore 

 elongate to a large degree. Since the blastopore forms well below 

 the edges of the dorsal marks, it becomes evident that most of 

 the initial movement results from the extension of the marks 

 into the blastopore and not from a movement of the dorsal lip. 

 A comparison of various eggs shows that the amount the lip 

 advances, as nearly as could be determined, varies from 20° to 

 35°. 



During recent years, a fairly general agreement has been reached 

 regarding the amount of movement of the dorsal lip of the blasto- 

 pore of the frog's egg. Kopsch ('95), by means of photographs 

 of the living egg, found that the dorsal lip formed 25° below the 

 equator and advanced 75° or thereabouts. Wilson ('01), from 

 pricking experiments, reached the same conclusion. Ikeda 

 ('02), working with Rachophorus, found that the dorsal lip ap- 

 peared 10°-20° below the equator. From pricking experiments, 

 he concluded that the advance was in the neighborhood of 70°. 

 Hence the blastopore closed above the lower pole. In Bufo and 

 Rana, his results were slightly different. Moszkowski ('02) 

 conducted, from some eggs in w^hich an exovate of unknown 

 origin was present, that the dorsal lip appeared 30° below the 

 equator and moved 75°. Miss King ('02), working with Bufo 

 lentiginosus, concluded from eggs studied by Pfliiger's method 

 that the blastopore lip advanced 140°. Morgan ('02) states 

 that the amount of the advancement of the dorsal lip is not cer- 

 tain, but he thinks it exceeds 75°. Todd ('04) found, in Rana 

 palustris, that the blastopore closed beyond the lower pole. 

 Assheton ('94) concluded that the advance of the lip was 60° 

 to 70°. Brachet ('03), on morphological grounds admits a lower- 

 ing of the lip. 



