VI.] THEIR SIGNIFICANCE IN HEREDITY. 371 



me to be almost a proof of the existence of such an arrangement, 

 for without this supposition the process would cease to have 

 any meaning. 



This is the only kind of karyokinesis which has been ob- 

 served until recently ; but if the supposed nuclear division 

 leading to a reduction in the number of ancestral germ-plasms 

 has any real existence, there must be yet another kind of 

 karyokinesis, in which the primary equatorial loops are not 

 split longitudinally, but are separated without division into two 

 groups, each of which forms one of the two daughter-nuclei. In 

 such a case the required reduction in the number of ancestral 

 germ-plasms would take place, for each daughter-nucleus 

 would receive only half the number which was contained in 

 the mother-nucleus. 



Now there is more evidence for the existence of this second 

 kind of karyokinesis than the fact that it is demanded by my 

 theory; for I believe that it has been already observed, although 

 it has not been interpreted in this sense. 



It is very probable that this is true of van Beneden's^ ob- 

 servation on the ^^,g of Ascaris niegalocephala : he found that 

 the nuclear division which led to the formation of the polar 

 body differs from the ordinary course of karyokinesis, in that 

 the plane of division is at right angles to that usually assunKid. 

 Carnoy ^ has confirmed this observation in its main features, 

 and he has made the further observation that out of the eight 

 nuclear loops which are found at the equator of the spindle, 

 four are removed with the first polar body, and that half of the 

 remaining four are removed with the second polar body. The 

 first of these two divisions would have to be looked upon as 

 a reduction, if it is certain that each of the eight nuclear loops 

 consists of different ancestral germ-plasms ; but this assump- 

 tion is impossible, although on the other hand it cannot be 

 directly disproved : for we are not able to see the ancestral 

 germ-plasms. But it must nevertheless be maintained that the 

 removal of the first four loops does not imply a reduction in 

 the number of ancestral germ-plasms in the nucleus ; because, 



' E. van Beneden, * Recherches sur la maturation de I'oeuf, la feconda- 

 tion et la division cellulaire.' Gand et Leipzig. Paris, 1883. 



■^ J. B. Carnoy, ' La Cytodierese de i'oeuf, la vesicule germinative et 

 les globules polaires de I'Ascaris megalocephala.' Louvain, Gand, 

 Lierre, 1886. 



B b 2 



