Artificial Parthenogenesis in Thalassetna Mellita 139 



bryo is never produced. I have never found a single instance of 

 the occurrence of the pseudo-trochophore described by Lillie and 

 others. It would seem true, therefore, that in the development 

 of Thalassema at all events, cell division is something more than 

 a mere '^ localizing factor;" it is rather, on the contrary, funda- 

 mental and essential to all processes of differentiation and cor- 

 relation. 



Not only does the conclusion just expressed seem to be the cor- 

 rect one, but it is also undoubtedly true that the more closely the 

 course of progressive cellular differentiation follows in the path of 

 the normal processes of development, the more nearly normal 

 is the resulting trochophore, both structurally and function- 

 ally. Abnormalities in cleavage at any stage seem to perma- 

 nently disturb the organization of the embryo, while the resulting 

 defects and deficiencies do not appear to be made good later 

 on. 



It is of interest to remark in this connection, that while differen- 

 tiation of the egg does not occur in the absence of cell division, 

 cytoplasmic cleavage in Thalassema does not appear to take place 

 without preceding division of the nucleus. From the most care- 

 ful examination of my sections, I have found no evidence that the 

 cytoplasm segments if unassociated with mitotic phenomena 

 involve a distribution of chromatin. This fact is not in accord 

 with the observations which have been frequently made on other 

 eggs, and may possibly be correlated to a certain extent with the 

 absence, or, at any rate, the very rare occurrence of cytastersinthe 

 eggs of my experiments. 



Finally, it may be remarked that, since the parthenogenetic 

 trochophores of Thalassema possess a highly normal organization 

 with a differentiated digestive tract, etc., a physiologically self- 

 sustaining organism would seem to be a possibility in the partheno- 

 genetic development of this worm, and that success in rearing the 

 larvae to maturity must depend upon the finding of satisfactory 

 means of nurture for tiding the animals over the critical period. 

 This accomplishment undoubtedly lies within the bounds of 

 experimental investigation. 



