52 HARRIETT M. ALLYN. 



up occurred, and some possible cleavage, but probably not 

 normal mitotic cleavage. In several of the experiments there 

 was a suggestion in the living material of a small amount of early 

 cleavage, but the next morning segmented swimmers were not 

 to be found, except in one set of experiments, when one possible 

 segmented larva appeared as a result of treatment with a solu- 

 tion of one drop of n/io KCN in 100 c.c. sea-water for one hour* 

 following 3.5 per cent. 2^4 M KC1 in sea-water for about 45 

 minutes, and another among the eggs left in the same KCN 

 solution for 2^ hours. Sections from this set of experiments 

 show much breaking up into small round masses, which may be 

 abnormal cells. The material is suggestive, but that is all. It 

 may be that the treatment causes a slight amount of cleavage 

 and some breaking up, but certainly rarely, if ever, like that of 

 normal development. It is interesting to note that in a number 

 of Ch&topterus experiments many lots of eggs which in early stages 

 are most suggestive of cleavage, in late stages show less differen- 

 tiation than in some other experiments. It may be that unless 

 the cleavage is normal, differentiation is more difficult with 

 cleavage than without it. 



8. Sodium Chloride and Sodium Hydroxide. To 8 c.c. of 2% M 

 NaCl + 50 c.c. sea-water, was added either 0.2, 0.4, or i.o c.c. 

 nfio NaOH 2 . The eggs were transferred to ordinary sea-water 

 after 20, 50, 75 and 120 minutes. Swimmers appeared in all the 

 dishes except, the 120 minute lot, and the i c.c. n/io NaOH lot for 

 20 minutes or 75 minutes. The best results were obtained from 

 the 0.2 c.c. n/io NaOH lot for 50 minutes. No cleavage was 

 noted. Something resembling a large polar body was formed, 

 similar to that seen in the sodium chloride treatment without 



sodium hydroxide. 



V. DISCUSSION. 



i . Problem of the First Changes.- The first changes in develop- 

 ment are initiated by the entrance of the egg into sea-water from 

 the ovary of the animal. This stage in the development consists 

 in the break-down of the germinal vesicle, the migration of its 

 contents to the animal pole, and the formation of the metaphase 

 of the first maturation spindle. The freeing of the vitelline 

 membrane from the surface of the egg, with the accompanying 



