398 



C. M. CHILD. 



by the division of the cleavage furrow into two (Fig. n). Such 

 cleavages occurred in about 40 per cent, of eggs placed in KCN 

 w/i,OOO for io}/2 hours before fertilization then well washed and 

 kept in sea water and fertilized one hour after removal from KCN. 

 Figs. 7-10 are drawn from such eggs. After this treatment there 



8 



10 



ii 



is no elevation of a fertilization membrane from the egg surface, 

 and the blastomeres frequently become entirely separated after 

 cleavage. Eggs placed in KCN w/ioo fifteen minutes after 

 fertilization and washed and returned to sea water after three 

 hours also showed cleavage of this kind in 30-40 per cent. In 

 the other eggs of these lots cleavage is normal or incomplete and 

 often irregular or else delayed with simultaneous formation of a 

 number of blastomeres. Apparently then these one-sided cleav- 

 ages represent the first step in departure from normal cleavage. 

 The indirect evidence shows that a susceptibility gradient is 

 present in these stages of development and that the region of 

 highest susceptibility and therefore of highest metabolic rate is 

 the apical pole. It is evident that cyanide inhibits cleavage, 

 and if the apical pole is most susceptible, we should expect to 

 find cleavage most completely inhibited there, and least inhibited 

 at the basal pole. It is probable, therefore, that these cleavage 

 furrows start from the basal and proceed toward the apical pole, 



