384 Erste Sektion: Cytologie und Protozoenkunde. Erste Sitzung. 



lining epithelium, which probably enters the egg through the 

 chorion, formed by those protoplasmic processes which are respon- 

 sable for the distinct radial striation of the chorion. 



Direction of Egg-Axis. Examination of the dia- 

 gram, fig. 34, pl. Ic, will give some idea of the different forms 

 of centers actually observed in microscopic sections. It will be 

 seen that some are typical centrosomes and asters. The point 

 of attachment of these eggs (actual cases selected at random), bears 

 no constant relation to the axis of the egg, indicated by a line 

 drawn through the center and the germinal vesicle. It is noti- 

 cable, also, that the axis of one egg bears no constant relation 

 to neighbouring eggs. Evidently gravity does not determine the 

 egg axis. 



That this egg axis is a real, not merely an imaginary axis, 

 is shown by the fact that when the egg matures, the germinal 

 vessicle moves toward the periphery, away from the center. The 

 largest accumulation of yolk is found around the center which 

 thus locates the vegetative pole. 



In the case of the epithelial cells lining the ovarian tube, 

 the polarity might be accounted for as a. result of contact or pres- 

 sure from neighbouring cells, perhaps. But the eggs seem to be 

 a law unto themselves in this regard, the axis being determined 

 by internal structures which, aside from the actual, visible evi- 

 dences of such structure, clearly point to an Organization which 

 does not in all matters and immediately adjust itself to external 

 influences; but offers such resistance to these, as to give the egg 

 an individuality and life of its own. 



General Impressions of Specific Charac- 

 t e r s. Besides such positive evidences of structure as I have 

 attempted to present, there are others which can neither be re- 

 presented in drawings, nor expressed in words. It is the general 

 effect or impression which one acquires gradually in a prolonged 

 study of this kind. 



It is sometimes affirmed in support of the view that chromo- 

 somes are the bearers of heredity, that it is possible to know one 

 species of organism from another merely by the appearance of 

 the chromosomes. It is safe to say that, besides the distinctive 

 features of the nucleus in each case, the general appearance of the 

 cytoplasm is different in different animals, notwithstanding the ge- 

 neral similarity in the cytoplasmic fibrils. The cytoplasm of Amoeba 

 differs as much from the cytoplasm of the egg of Limulus as the 

 Amoeba itself differs from the egg. It is possible to identify Clem- 

 mys marmorata or Astacus fluviatilis by an microscopic exami- 

 nation of the cytoplasm of their eggs. But just what the distin- 

 guishing features are, can better be feit than described, after a 

 prolonged study of the subject. 



