No. 644] ARRESTED EVOLUTION 



265 



rapidity, Apus cancriformis reaching in two weeks a full 

 size up to five inches,^ produce an enormous number of 

 eggs and die. 



The origin of parthenogenesis in these forms as well 

 as in the rotifers and certain insects has been fully dis- 

 cussed by Geddes and Thompson, and they are certain 

 that it has originated as a degeneration from the ordi- 

 nary sexual process {ibid, p. 198) and is no direct 

 persistence of a primitive ideal state. Their theory of 

 parthenogenesis is that the ova that develop partlieno- 

 genetically " are to be regarded as incompletely differenti- 

 ated female cells, which retain a measure of katabolic 

 (relatively male) products, and thus do not need fertil- 

 ization " (they form only one polar body). "Such a 

 successful balance between anabolism and katabolism is 

 indeed the ideal of all organic life. In parasitic fungi, 

 sexual reproduction disappears, and surrounding waste 

 products presumably help the purpose otherwise effected 

 by sexual organs, so peculiarities in the conditions of 

 parthenogenetic ova may explain the retention of the 

 normal balance which makes division possible without the 

 usual stimulus of fertilization. Abundant and at the same 

 time stimulating nutrition (Rolph), early differentiation 

 of the sex-cells (Simon), the general preponderance of 

 reproductive over vegetative constitution (Hensen), their 

 liberation before the anabolic bias has carried them too 

 far, are among these favoring conditions." 



Parthenogenesis thus appears as a degenerative asex- 

 ual process arising from peculiar conditions, the most 

 important of which appears to be temporary over-nutri- 

 tion. As in the other asexual modes of propagation, 

 in division and budding, the inference suggests itself 

 readily that this suppression of fertilization must induce 

 persistence, for as Geddes and Thompson point out (ibid., 

 p. 193) the establishment of parthenogenesis and the ab- 



Hermanni Ml. Brgt bei Strassburg im September 1912," Mitt, der PhUo- 

 mat. Gesellsch. in EJsass-Lothringen, Bd. 4, Heft. 5, Jahrgang 1912; 1913, 



