708 



THE AMERICAN NATURALIST 



[Vol. LI 



this antf^ they may aid in changing the substances fur- 

 nished by the nurse cells into material available for the 

 embryo or they may have something to do with the for- 

 mation of yolk."^^ It is also possible that they may con- 

 trol differentiation in the peripheral layer of cytoplasm 

 and thus provide a method of nuclear control of the or- 

 ganization of the egg. The last hypothesis may be ob- 

 jected to on the grounds that the secondary nuclei appear 

 to be irregularly distributed and that they are known to 

 occur in only a few species of insects. 



Another possible way in which the initial organization 

 of the insect egg may arise is through the activities of 

 mitochondria. The rather constant presence of these 

 bodies in the cytoplasm of almost all types of cells indi- 

 cates that they may be of considerable importance in the 

 process of differentiation. If they take part in the gen- 

 esis of egg organization they then may play the role 

 attributed to them by certain investigators of being the 

 cji;oplasmic bearers of hereditary factors corresponding 

 in this respect to the nuclear bodies of similar function, 

 the chromosomes. 



The most striking differentiation in the cytoplasm of 

 the insect egg is that which involves the germ-line deter- 

 minants. As stated above, we do not know for certain in 

 any case the origin of the peculiar cytoplasmic mass that 

 contains these determinants, but a number of hypotheses 

 have been suggested. In Miastor, for example, the fol- 

 lowing is offered to account for the appearance of the 

 "pole-plasm" in the fully developed oocyte.'^- 



It may be (li^tiii<riu<.lH'.I fn n t'l. 

 tion at the posterior end ;ui.l h. r.iib 

 appears shortly before ilic uuiiiii 



, .'utn'iu i< ."',,1.1,1 dyes. It 



