EEPRODUCTION OP APHIDES. 107 



Even before the time of Reaumur's and Bonnet's 

 discoveries it had been asserted that the unimpreg- 

 nated egg of some Papilionidas had proved fertile, but 

 such novel observations met with but scant attention ; 

 firstly, perhaps, from incredulity as to the fact, and 

 secondly, from a notion that such was contrary to all 

 experience. 



Here the subject seems to have rested for nearly 

 one hundred years. The phenomenon of multiplica- 

 tion by fission observed by Trembley in the fresh- 

 water Hydra was too recent and peculiar to cause the 

 naturalists of his day to infer analogous processes in 

 Insects. Still an attempt towards an explanation was 

 made with reference to Aphides both by Leuwenhoeck 

 and Cestoni, who considered that these insects were 

 hermaphrodite; and this belief accorded with the 

 views of the best zoologists of that day. 



Bonnet substituted another explanation, and argued 

 that the chief difference between the viviparous and 

 oviparous female consisted in the more or less perfect 

 development of the two forms. According to his view, 

 the conjunction of the male gave to the germ that 

 which the mother, on account of her incomplete 

 development, was unable to supply to her progeny. 

 Abundance of food, and a high temperature, he 

 thought, produced the first form ; cold and insufficient 

 food in autumn caused the appearance of the egg- 

 laying female, viz. the second form.* 



Trembley attacked the subject differently. He con- 

 sidered that the influence of the male in autumn 

 transmitted itself throughout the whole generation of 

 females of the following year ; and this view, more or 

 less modified, was accepted by Dutrochet, and by 

 Kirby and Spence, who all rejected the hypothesis of 

 hermaphroditism. 



Reproduction amongst animals may occur through 

 several processes, all of which are in a measure 

 analogous to the propagation of vegetables. Amongst 



* Bonnet, ' Considerations sur les corps organises,' t. ii, 1776. 



