POLARITY OF THE CELL 



57 



But, although this conception of polarity has an entirely different 

 point of departure from Van Beneden's, it leads, in some cases at 

 least, to the same result ; for the cell-axis, as thus determined, may 

 coincide with the morphological axis as determined by the position 

 of the centrosome. This is the case, for example, with both the 

 spermatozoon and the ovum ; for the morphological axis in both is 

 also the physiological axis about which the cytoplasmic differentia- 

 tions are grouped. Recent researches have further shown that the 

 same is the case in many forms of epithelia, where the centrosomes 

 lie in the outer end of the cell, often very near the surface. 1 (Fig. 23) 



Fig. 23. Centrosomes in epithelial and other cells. [A, D, ZlMMERMANN; , HEIDENHAIN 

 and COHN; F, HEIDENHAIN.] 



A. From gastric glands of man ; dead cell at the left. B. Uterine epithelium, man. C. From. 

 human duodenum ; goblet-cell, with centrosome in the middle. D. Corneal epithelium of monkey.. 

 E. Epithelial cells from mesoblast-somites, embryo duck. F. Red blood-corpuscles from the duck- 

 embryo. The centrosomes are double in nearly all cases. 



and the recent observations of Henneguy ('98) and Lenhossek ('98,1) 

 give reason to believe that the " basal bodies" to which the cilia of 

 ciliated epithelium are attached may be the centrosomes. 2 These 

 facts are of very high significance ; for the position of the centre- 

 some, and hence the direction of the axis, is here obviously related 

 to the cell-environment, and it is difficult to avoid the conclusion that 

 the latter must be the determining condition to which the intracellular 

 relations conform. When applied to the germ-cells, this conclusion 

 becomes of high interest ; for the polarity of the egg is one of the 



Zimmermann, '98; Heidenhain and Cohn, '97. 



2 Cf. p. 356. 



