218 



THE CELL 



surface in any of the diameters, but in an oval disc it is parallel 

 only to the longest diameter. 



The phenomena observed during cell division, and especially 

 daring the formation of the farrows, are almost without exception 

 in accordance with these laws. Two facts, however, are especially 

 confirmatory of the truth of the second law ; one was discovered 

 by Auerbach, through his experiments on the eggs of Ascaris 

 nigrovenosa and Strongylus auricularis (VI. 2), and the other by 

 Pfliiger. 



The eggs of both the Nematodes investigated by Auerbach are 

 oval in shape (Fig. 110), so that two poles can be distinguished in 



FIG. 110. Eggs of Ascaris nigrovenosa, in four different stages of fertilisation. (After 

 Auerbach, PI. IV., Figs. 8-11.) 



them, and these two poles play different roles during fertilisation. 

 At the one at which the germinal substance of the egg is situated, 

 the pole cells are formed, and the female pro-nucleus develops, 

 whilst at the other pole, which faces the mouth of the uterus, the 

 spermatozoon enters, and fructification occurs ; further, the male 

 pro-nucleus makes its appearance here (vide Chap. VII.). 



Whilst gradually increasing in size, both pro-nuclei approach 

 each other, travelling in a straight line, which coincides with the 

 axis of the egg ; finally, after having grown into two vesicles of 

 considerable size, they meet in the centre of the axis ; they then 

 come into such close contact that their contingent surfaces become 

 flattened (Fig. 1104). 



As a rule, during the conjugation of the sexual nuclei, the axis 

 of the spindle, which develops out of them, and at the ends of 

 which the centrosomes are situated, lies somewhere in the 



