ROBERT CHAMBERS 35 



jellied state and vice versa. The protoplasm must have its phase 

 relations in a delicately balanced state in order that this may occur. 

 In the egg we have seen that the reversal to a jellied state is probably 

 accompanied by a separating out of a liquid. Something in this 

 liquid may possibly control, in periodic rhythms, the physical state 

 of the protoplasm surrounding it. We may assume that as long as 

 there is a quantity of this substance localized in the egg it can induce 

 aster formation. The idea suggests itself that one purpose of the 

 spermatozoon is to accumulate this substance. In the mature unfer- 

 tilized egg there is no localized area from which the jellying process 

 may spread. The entrance of a sperm furnishes a focus as it were. 

 Around this focus an aster develops with a steady accumulation of the 

 liquid in its center. This liquid area surrounds the nucleus and puts 

 the egg in a condition similar to that of a blastomere. The process of 

 cleavage then becomes the same in both. 



An interpretation disconsonant with previous ones concerning the 

 mode of aster formation in artificially parthenogenetic eggs has been 

 recently put forward by Herlant.* Wilson^ in Toxopneustes, had 

 long ago shown that eggs treated insufficiently with a parthenogenetic 

 agent may form monasters which disappear and reappear in several 

 successive rhythms. Hindle^ found this to be true also for the sea- 

 urchin egg, if treated with butyric acid alone. A sufficient treatment, 

 however, of a parthenogenetic agent results in the disappearance of 

 the monaster followed by the appearance of an amphiaster. This 

 results in cleavage of the egg. In the sea-urchin egg, the butyric 

 acid treatment has to be followed by a bath of hypertonic sea water 

 in order that this may occur. The hypertonic treatment often results 

 in the formation of several cytasters in the egg. The cytasters pro- 

 duced by the hypertonic treatment Herlant claimed to be due to 

 dehydrative effects producing spots within the egg cytoplasm about 

 which the asters appear. Herlant assumed that one of these cytas- 



* Herlant, M., Comment agit la solution hypertonique dans la parthenogenese 

 experimentale (method de Loeb). I. Origine et signification des asters accessoires. 

 Arch. Zool. exp. et gen., 1918, Ivii, 511; II. Le mecanisme de la segmentation. 

 Arch. Zool. exp. et gen., 1919, Iviii, 291. 



^ Hindle, E., A cytological study of artificial parthenogenesis in Strongylo- 

 centrolus purpuratus, Arch. Entwcklngsmechn., 1910-11, .xxxi, 145. 



