716 



THE AMERICAN NATUEALIST 



[Vol. LI 



an influence upon the cytoplasm during the oogonial and 

 growth periods of the egg, and a study of the genesis of 

 cytoplasmic organization may lead to data that will help 

 us solve this difficult problem. 



If the polarity of the oocyte when recognizable is not 

 inherited, i. e., if it is not transmitted to the primordial 

 germ cells by the egg, and retained by the oogonia, it 

 must arise de novo just before or during the growth 

 period. One observer^"^ has found that in certain beetles 

 the position of the spindle remains, resulting from the 

 differential divisions that precede the formation of the 

 oocyte, indicates the polarity of the ultimate organism, 

 but he does not tell us how this ''polarite predifferen- 

 tielle" is brought about. In all insects the end of the egg 

 directed toward the head of the mother becomes the an- 

 terior end of the offspring. This is also the pole of the 

 egg lying next to the nurse cells or that is closest to the 

 nurse-cell chamber. This relation between oocyte and 

 nurse-cells may be the determining factor in the polarity 

 of these eggs and, if so, would indicate that polarity here 

 is due to environment. How this relation could influence 

 the polarity may l)e exi)lained by means of axial gradi- 

 ents of metabolism, such gradients in this case being 

 produced by greater external stimulation at the end near 

 the nur&e-cell chamber where nutritive substances are 

 elaborated and added to the oocyte. By this theory of 

 metabolic gradients, differentiation along an antero- 

 posterior axis can be accounted for and further differen- 

 tiations of a morphological and physiological nature 

 would result from "chemical transportative correlation 

 between the different ]>arts."^^' 



We should not lose sight of the fact, liowever, tliat these 

 hvpothecated phvsiohigical activities require proto])la>m 

 a", a material ba^-^ and that their results depend upon the 

 charart.M- ..t' thi^ prntopla^ni. If polnritv ...tahli^hed 

 at th. Mnu. Mi.u.-M.-l alM,v.. it U^\.^^^ a hmu ..ries of 

 nurhM,-r>toi>laMiii( interaction^ uhirl, haxr n.. (h.iiht re- 

 sulted in the differentiation and h.calization of numerous 



« Govaerts, 1913, Arcli. Biol, Tome 28. 



