MATURATION AND AMPHIMIXIS 441 



Van Beneden, that each germ-cell is originally hermaphrodite, 

 and that the maturation processes imply the removal of male 

 qualities from the ovum and of female qualities from the sper- 

 matozoon, has been abandoned ; and the reducing divisions are 

 recognised as securing a constancy in the number of chromo- 

 somes characteristic of each species, for without some such pre- 

 liminary reduction the number would obviously be doubled at 

 each fertilisation. That a reduction does really occur in both 

 plants and animals seems now incontrovertible, but the precise 

 manner of the reduction seems to differ considerably in different 

 organisms. It should be noted, moreover, that in some par- 

 thenogenetic ova — e.g. of Aphides — only one polar body is 

 formed and no reduction in number is effected ; while in other 

 parthenogenetic ova — e.g. those eggs of bees which develop 

 into drones — two are formed : a strange fact, in part at least 

 explained by Brauer, who showed that in the parthenogenetic 

 ova of Artemia both types occur, but that when two polar 

 bodies are formed the second remains in the e^g and behaves 

 practically like a sperm-nucleus. 



Minute inquiries have gone so far that it is possible to assert 

 that in some cases the young germ-cell has an equal number 

 of paternal and maternal chromosomes. And similar minute 

 inquiries — which almost baffle us with their intricacy — make 

 it exceedingly probable that in the reduction divisions maternal 

 chromosomes separate from paternal chromosomes, and yet 

 not so thoroughly that all the paternal chromosomes pass into 

 one cell and all the maternal into another. If this be true, 

 we can better appreciate the importance of the reduction- 

 divisions which occur in maturation, for they afford opportunity 

 for new permutations and combinations of hereditary qualities. 

 They do not originate anything new, but they shuffle the cards, 

 so to speak. In some cases, at least, it seems quite certain that 

 entire chromosomes are separated off into different cells, into 

 polar bodies which come to nothing, or into other sperma- 



