VI.] THEIR SIGNIFICANCE IN HEREDITY. 379 



by the parthenogenetic or the sexual method ; siicli decision 

 being brought about, as was shown above, by the fact that only 

 one polar body is expelled in the first case, while two arc ex- 

 pelled in the second. But if we are obliged to assume that 

 reproduction by means of fertilization, necessarily imjilics a 

 reduction to one half of the number of ancestral gcnn-plasms 

 inherited from the parents, — the further conclusion is obvious, 

 that the second division of the egg-nucleus and the expulsion 

 of the second polar body represent such a reduction, and that 

 this second division of the egg-nucleus is unequal in the sense 

 mentioned above, viz. one half of the ancestral germ-plasms 

 remains in the egg-nucleus, the original number being subse- 

 quently restored by conjugation with a sperm-nucleus; while 

 the other half is expelled in the polar body and perishes. 



I may add that observations, so far as they have extended t() 

 such minute processes, do indeed prove that the number of 

 loops is reduced to one half It has been already mentioned 

 that, according to Carnoy, such reduction occurs in . I scan's 

 megahcep/iala, but the same author also describes the process 

 of the formation of polar bodies in a large number of other 

 Nematodes^ ^ and his descriptions show that the process occurs 

 in such a way that the number of ancestral germ-plasms must 

 be reduced by half. Sometimes half the number of primary 

 loops pass into the nucleus of the polar body, while the other 

 half remains in the egg. In other cases, as in Ophiostoiuum 

 mucronahitn, the primary nuclear rods divide transversely,— a 

 process which must produce the same effect. It is true that 

 these observations require confirmation, and since, with un- 

 favourable objects, the difficulties of observation are extremely 

 great, there may have been errors of detail; but I do not think 

 that there is any reason for doubting the accuracy of the 

 essential point. And this essential point is the fact that the 

 number of primary loops is divided into half by the formation 

 of the polar body. 



But even if we could not admit that such a conclusion is 

 securely founded, it cannot be doubted that the formation of 

 the second polar body reduces to one half the quantity of the 



1 Carnoy, 'La Cytodierese de foeuf; la vesiculc gcrminative et les 

 globules polaires chez quelques Nematodes.' Louvaiu, Gaud, I-ierrr. 

 1886. 



