DEGENERATE SEXUAL REPRODUCTION. x 6i 



lized by Italian or Cyprian drones, produced hybrid females but pure 

 drones, a proof that on the latter the sperm does not operate." Again, 

 it sometimes happens that what are called " fertile workers" crop up, 

 which in consequence of some accident or misdirected intention in 

 the nutrition, become less abortive than the host of semi-females 

 which make up the body of workers. They are fertile enough to 

 lay eggs, but their female organs do not seem to admit of their being 

 impregnated. Certain it is that they only produce drones. What 

 has just been said in regard to bees, is also true of some wasps and 

 ants. 



(e) Seasonal Parthenogenesis. — In some of the minute aquatic 

 crustaceans (C/adoeera), popularly included under the general title 

 of water-fleas, parthenogenesis only occurs for a season, and is peri- 

 odically interrupted by the birth of males, and the occurrence of the 

 ordinary sexual reproduction. Males generally reappear in the disad- 

 vantageous conditions of autumn, but Weismann denies^that there 

 is a direct connection between these facts. The jztommon aphides are 

 parthenogenetic for a succession of generation^, sometimes as many 

 as fourteen, throughout the summer, but the-'cold and hard times of 

 autumn bring back the males and the sexual process. The fertilized 

 egg lives on through the winter, and develops with the warmth of 

 the next spring. By keeping up the temperature and nutritive 

 optimum for three or four years in the artificial summer of a glass 

 case, Reaumur and Kybur succeeded in rearing as many as fifty con- 

 tinuous parthenogenetic generations. In the gall-wasps {Cynipidte) 

 there is usually only one parthenogenetic generation between the 

 normal sexual reproductions, but in many insects besides aphides 

 there are several. It ought to be noted that the parthenogenetic 

 aphides are hardly at the same structural level as the females which 

 are fertilized; but as the differences mainly lie in the absence 

 of certain accessory genital organs, there is no reason for regarding 

 the parthenogenetic forms, as some have done, as larval. 



(./ ) Juvenile Parthenogenesis. — Cases do occur, however, where 

 larval forms become precociously reproductive (as sometimes happens 

 among higher organisms), and produce offspring parthenogenetically. 

 Such precocious production of parthenogenetic ova must be distin- 

 guished from the entirely asexual reproduction exhibited by many 

 larvae. No very firm line indeed can be drawn, but in the last cases 

 no cells which can be called ova are present. In 1865 Professor N. 

 Wagner observed what has been much studied since, that in the larvae 

 of some two-winged or dipterous midges (for example, Miaslor), the 

 cells of the reproductive rudiment develop into larvae within the 

 mother-larva's body. The mother falls victim to her precocity, for the 



