EXPERIMENTS WITH FROG'S EGGS. 83 



April 13, 9 a. m. Same condition ; possibly another division 

 has occurred. 



April 13, 6 p. m. Some of the eggs have divided further. 

 Large blastoccel (Fig. 21). 



April 14, 9 a. m. Same as last. 



April 14, 5:15 p. m. A large and irregular segmentation 

 cavity, lying more on one side, is seen in sections (Fig. 22). 



April 15, 9 a. m. The surface of the egg shows white flecks, 

 and the cells have divided further. Large blastoccel present. 



April 1 6, 2 p. m. Same. Cells irregular. Segmentation 

 cavity large. 



April 1 8, 9 a. m. Same. Large segmentation cavity. No 

 downgrowth of small cells. Yolk irregularly divided (Fig. 23). 



April 20, 9 a. m. Divided further. Top of egg brown instead 

 of black. Large and irregular segmentation cavity (Fig. 24). 



April 22, 93. m. In the surface view the outlines of the upper 

 dark cells are very irregular. Large segmentation cavity sur- 

 rounded by irregular cells (Fig. 25). 



Compared with the normal set, 1 put up at the same time, the 

 retardation of this cold series is apparent. After eleven days 

 these eggs on the ice did not develop further than those at room 

 temperature in twenty-four hours. Not only is there a delay, 

 but the development has become quite abnormal, especially dur- 

 ing the later stages. The sections show that the cells have in 

 general an irregular outline, and are not compacted together as 

 in the normal embryo. There is no downward migration of the 

 material of the top of the egg, hence the abnormal forms of 

 embryos described in my former paper. Great differences and 

 abnormalities are found in the formation of the segmentation 

 cavity, and this same difference was noticeable in the older stages. 

 These older stages have been described in my earlier papers. 



THE EARLY DEVELOPMENT OF LITHIUM LARV/E OF THE FROG. 



In a previous paper 2 I have described some of the effects of 

 lithium solutions on the development of the frog's egg. The 



1 The control normal set are those described in my forthcoming paper on " The 

 Origin of the Embryo-Forming Materials in the Frog's Embryo," 1906. 

 * Roux* s Archiv, XVI., 1903. 



