452 WM. E. KELLICOTT 



from the normal in being smaller, that is in containing less pro- 

 toplasm, and in being markedly more convex. This increase in 

 convexity may simply indicate a decrease in surface tension di- 

 rectly due to the lower temperature. If the temperature be not 

 lower than about 12°C. cleavage continues slowly and with little 

 or no apparent abnormality, save that the blastomeres, like the 

 germ-discs, are smaller and unusually convex, and therefore 

 more than normally separated from one another. ' Stages of 

 eight to sixteen cells may be found Iwenty-four to thirty-six 

 hours after fertilization. 



At a temperature of about 8-10°C. the effects are quite varied. 

 In the first place, in a considerable and widely variable propor- 

 tion of the eggs no true germ-disc is formed, cleavage rarely 

 occurs, and after a time the protoplasmic parts become wholly 

 vacuolated, giving no sign of living processes, either during con- 

 tinued treatment to cold or after their removal to a higher tem- 

 perature. Other eggs, however, are not killed by this treat- 

 ment; a few may form small germ-discs and cleave regularly 

 once or twice during twenty-seven to thirty hours. Or cleavage 

 may become very irregular, blastomeres later showing wide differ- 

 ences in size and extensive divergences from the typical arrange- 

 ment. Many instances were noted where the germ-disc was 

 very imperfectly formed, the thin protoplasmic cap remaining 

 spread over one-fourth to one-third of the egg, with occasional 

 mounds, cell-like though without cell-walls, scattered irregu- 

 larly over it. In still other ins trances there were no true cellular 

 structures whatever present, even after several days, and aggre- 

 gations of nuclear substance might be seen scattered promiscu- 

 ously through a cytoplasmic mass of irregular form. Several 

 eggs were noted in which the protoplasm had collected in sev- 

 eral distinct and widely separated regions. After several days 

 all these eggs showed at least two kinds of material derived from 

 the cytoplasmic part of the egg; one was dark and granular, 

 quite opaque but still apparently active, the other clear and 

 vacuolated and apparently no longer hving. 



It should be noted that throughout this paper the appearances 

 described are those given by microscopic examination of total, 



