BLASTOGENIC VAEIATIONS. 177 



Parthenogenesis. We saw in the last chapter that 

 Weismann regarded sexual reproduction as a potent 

 factor in the production of variations, in that it af- 

 forded inexhaustible supplies of fresh combinations of 

 the individual variations already represented in the 

 mingling germ-plasms. We should accordingly con- 

 clude that when such sexual union is wanting, as in 

 parthenogenetically produced animals, the amount of 

 variation will be smaller, and that parent and offspring 

 will more closely resemble each other. The evidence 

 upon this point is exceedingly slight, but what there is 

 perhaps tends rather to support this deduction. Thus 

 Weismann made a series of observations, extending 

 over eight years, upon a small ostracod, Cypris reptans. 

 This organism exists as two well-marked varieties, one 

 being coloured yellow, with five small green spots on 

 each side of the shell, and the other seemingly dark 

 green, owing to the great enlargement of these spots.* 

 Both varieties are produced parthenogenetically in the 

 neighbourhood of Freiburg, males never being found. 

 Females of each variety were isolated, fed well, and 

 allowed to multiply for many generations. It was 

 found that " the descendants of the same mother re- 

 sembled one another as well as the parent with which 

 the experiment began, even as regards minute details 

 of the markings. The differences were mostly as small 

 as those which may be observed in identical human 

 twins." Even after many generations no modification 

 showed itself, so that colonies were obtained which 

 could not be distinguished from their ancestors 40 gen- 

 erations back. In three different instances, however, 

 * ' Germ-Plasm," p. 344. 



