98 PETER OKKELBERG. 



separates after fertilization from the inner surface of a thin 

 preexisting membrane and the change does not seem to be due 

 to changes in the fertilization membrane but to changes in the 

 surface film of the egg. The egg of Asterias after separating from 

 the membrane was found to be smaller -than before. In case of 

 the lamprey egg also the initial change seems to be in the cortical 

 layer of the egg and not in the membrane. 



I have succeeded in inducing the egg of the lamprey to go 

 through changes similar to those it exhibits after fertilization, by 

 subjecting it to artificial stimuli, such as shaking, pricking with a 

 needle, exposing to sudden changes of temperature, etc. The 

 membrane separates in a similar manner f om the egg, a peri- 

 staltic wave passes over it and it becomes spherical in shape. 

 This indicates that the stimulus that starts the egg on a career 

 of development need not be of any specific kind. Some of the 

 lamprey eggs that have thus been stimulated have segmented 

 parthenogenetically. Bataillon 1 has succeeded in inducing par- 

 thenogenetic development of the egg of Petromyzon planeri by 

 introducing them into a 'solution of cane sugar, and he has dem- 

 onstrated that the segmentation is real and not merely a 

 fragmentation of the egg. 



Most of the material that the eggs lose as a result of fertilization 

 is probably water, but it seems to be certain that other substances 

 are also given off. Reighard (loc. cit., page 105) called the fluid 

 contents of the alveoli of the cortical layer in the egg of the wall- 

 eyed pike "cortical drops" and came to the conclusion that these 

 drops consisted of an albuminous substance and that this substance 

 is in solution in the perivitelline fluid. F. R. Lillie (loc. cit., page 

 365) thinks that the contents of the cortical alveoli in the egg of 

 Nereis are unquestionably colloidal. Similar conclusions have been 

 reached by others in other forms. In the lamprey egg after fertili- 

 zation much of the substance that fills up the space between the egg 

 and the membrane is water that has diffused through from the 

 outside. Some of the substance, however, came from the cortical 

 alveoli and is probably a colloid. F. R. Lillie 2 has found that 

 the unfertilized ova of Nereis and Arbacia in sea water secrete 



1 Bataillon, E., Arch. f. Entwicklungsmechanik, Vol. 18, 1904. 



2 Lillie, F. R., Science, N.S., Vol. 38, 1913. 



