152 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



earlier phyletic stage : we cannot offer such an interpretation 

 because this single polar division is found in all regular par- 

 thenogenetic eggs in which it has hitherto been sought for. It 

 has been found, it is true, in eighteen species only, but these 

 belong to different groups of the animal kingdom, viz. in eight 

 Daphnids, a Branchiopod, two Ostracodes, three Rotifers, and 

 four Insecta. In each of these a single polar body corresponding 

 to those of the other seventeen, is expelled, and in each we 

 must conclude that an apparently useless doubling of the idants 

 takes place, together with an ensuing diminution to half, as is 

 shown in the accompanying diagram (Fig. VIII), in which the 

 normal number of idants has been fixed at four, in order to 

 facilitate the comparison with Figs. I. and II. In view of the 



MEi2 



Fig. VIII. 

 Diagram of the maturation of the parthenogenetic q.%^. 



regular occurrence of the phenomena in all the cases which 

 have been examined, it is worth while enquiring whether a 

 meaning and significance are not to be attributed to these most 

 unexpected processes. 



In the first chapter the attempt was made to show that the 

 significance of the two ' reducing divisions,' in male and female 

 germ-cells, is a double one, first, the diminution of the ids to 

 half, and, secondly, the arrangement of the idants in fresh com- 

 binations. The first object might be gained by a single nuclear 

 division, but the second would be attained only very incom- 

 pletely, because a fresh combination of the idants occurs most 

 readily, when associated with a previous doubling in number. 



