CHAPTER XIII. 



Degenerate Sexual Reproduction or Parthenogenesis. 



§ I. History of Discovery. — From very early times there appears 

 to have been an impression, that in exceptional circumstances 

 reproduction might occur without fertilisation. Even Aristotle 

 gave reasons for believing that, without sexual union, the un- 

 fertilised eggs of the honey-bee might give rise to perfect adults. 

 We now know that he was right, in his conclusion at least, so 

 far as the development of drones is concerned. In the early 

 belief in Luci^ia sine conaibitii, much that was erroneous was 

 intermixed with a prevision of the truth; nor could we expect at 

 an early date that asexual multiplication {i.e., apart from ova alto- 

 gether) would be kept distinct from what we now mean by 

 parthenogenesis, or the development of ova without union with 

 sperms. In 1701, Albrecht observed that a female silkmoth, 

 which had been isolated in a glass case, laid fertile eggs ; and 

 though this vv'as for long discredited, the occasional partheno- 

 genesis of this insect has been repeatedly confirmed by com- 

 petent observers. 



In 1745, the ingenious Bonnet drew attention to what is 

 now a very familiar fact, the successive generations of virgin 

 plant-lice or Aphides. Throughout the summer, he observed 

 the production of numerous generations of these little insects, 

 all females, necessarily therefore all virgins, and yet fertile. So 

 strange did the fact appear, that it was for long utterly dis- 

 credited. Reaumur eluded the difficulty, by affirming that the 

 Aphides were hermaphrodite ; but Dufour soon proved that this 

 was erroneous, though he could only confess his ignorance in 

 referring the phenomena to " spontaneous or equivocal gen- 

 eration," in which "the act of impregnation was in no degree 

 concerned." The facts, however, were repeatedly re-observed. 

 Kirby and Spence admitted them as incontestable, but could 

 regard them only as " one of the mysteries of the Creator, that 

 human intellect cannot fully penetrate." 



