360 EYCLESHYMER. [Vol. X. 



Van Beneden ('83) observed this to be true not only in the 

 unsegmented but also in the unfecundated ^^^ of Ascaris. 

 •' Un examen attentif de la forme exterieure de I'oeuf, et plus 

 encore I'^tude de sa structure, demontrent I'existence dans ces 

 oeufs d'un axe morphologique, dont les extr^mites, que j'appelle 

 les p61es de I'oeuf, presentent une valeur tout differente tant 

 au point de vue anatomique qu'au point de vue physiologique. 

 L'un de ces poles est predestine k recevoir le zoosperme : 

 par ce point seul I'element f^condateur peut p6n6trer dans le 

 vitellus." 



One is accordingly forced to believe that we must assume a 

 polarity not only in the unsegmented ^g'g, but at a much earlier 

 period, even preceding fecundation. 



Mark ('90) has shown that in Lepidosteus the ovarian egg 

 early exhibits a polar differentiation, indicated by a secretory 

 activity of the protoplasm at a point which corresponds to the 

 future micropyle. 



In this connection the observations of Stauffacher ('93) on 

 the eggs of Cyclas are of interest. There is a certain area, 

 over which the ^^^ membrane does not extend, which later 

 becomes the micropyle. Stauffacher found this area to be the 

 point by which the early egg-cell is attached to the follicular 

 wall; one pole of the ^g^, is thus pre-determined in the germinal 

 epithelium. 



One of the most noticeable features in the central nervous 

 system of the larva of Amblystoma is the polarity of the nuclei 

 indicated by the peculiar eccentric position of the chromatin. 

 Mall ('93) likewise noted its presence in the cells of the retina 

 of Amblystoma, and considered its importance in the develop- 

 ment of the nerve fibre. 



Rabl ('89) has called attention to a polarity existing in the 

 nuclei of the epithelial cells of the Salamander. 



In the nuclei of the intestinal gland cells of Ptycoptera, Van 

 Gehuchten ('89) has observed this polarity and emphasized its 

 importance. 



The above facts not only indicate that the ovic axis is estab- 

 lished at a very early period, but also that this is one of the 

 most fundamental characters of animal cells; and we may con- 



