STUDIES ON GERM CELLS 481 



verbraucht; clieser wircl dem Zentrosoma geniihert unci umschliesst 

 es wie mit einer Kappe, so class er im optischen Durchschnitt stets 

 Hufeisen oder Sichelform aufweist. Infolge clavon wircl die wirkung 

 dieses Zentrosomas auf das Zellplasma nur sehr schwach, dieses Zen- 

 trosoma kann nur einen kleinen Plasmateil beherrschen, und die result- 

 ierende Zelle wird viel kleiner, als die Schwesterzelle. Diese kleine 

 Zelle, die den besonderen Korper bekommen hat, liegt naher zum 

 vegetativen Poles, als die grossere Schwesterzelle, und stellt die erste 

 Urgeschlechtszelle G (d"i), die grossere Schwesterzelle die erste Urento- 

 dermzelle E (d"^) vor (p. 231). 



In Ascaris, certain copepods, Sagitta, Polyphemus and certain 

 Daphnidae, the Keimbahn-determinants are not segregated in 

 one cleavage cell after about the thirty-two cell stage, but their 

 substance is distributed at the next division between the daugh- 

 ter cells. In the insects, such as Chironomus, Miastor and Chry- 

 somelid beetles, where, on account of the superficial cleavage, 

 the Keimbahn-determinants are not segregated in blastomeres, 

 the primordial germ cells, from the beginning, consist almost 

 entirely of the Keimbahn material or this material plus the 

 matrix in which it is imbedded. Hence in these cases the Keim- 

 bahn-determinants are localized at a determined point during 

 each cleavage stage, instead of being carried about by the move- 

 ments of the egg contents or of the blastomeres, but, as in the 

 eggs which undergo total cleavage, the determinants are dis- 

 tributed between the daughter cells as soon as the primordial 

 germ cells are established. The reason for this appears to be 

 that localizations occur in holoblastic eggs at each cleavage and 

 that not until the thirty-two cell stage or thereabouts does the 

 Keimbahn material become entirely separated from other organ- 

 forming substances and segregated in a single cell. When this 

 point is finally reached this Keimbahn material must necessarily 

 become divided between the daughter cells. 



In practically all known cases the daughter cells of the pri- 

 mordial germ cells are equal in size and each receives an equal 

 portion of the Keimbahn-determinants. This is certainly to be 

 expected from their constitution and future history. Sagitta, 

 however, differs in this respect for the remains of the 'besonderer 

 Korper' appear to be unequally distributed between the two 



