REPRODUCTION EXTRAORDINARY. 53 



shoots, rapidly increase in size, and soon come to maturity. In this 

 state is it found that the whole brood, without a single exception, 

 consists of females, or, let us say, of individuals capable of reproduc- 

 ing their kind. In a short time these animals give birth directly, 

 and without the deposition of eggs, to a second brood of females 

 like themselves, which again produces a third brood in the same 

 way, and of precisely the same description ; and this process goes 

 on throughout the summer without the appearance of a single 

 male insect. In the autumn, however, insects of both sexes are 

 again produced, and the females deposit eggs, to continue the 

 species in the same manner through the next summer. 



Tliis extraordinary mode of reproduction amongst the Aphides 

 was first made known by Bonnet, who traced the development 

 of nine successive generations of the asexual forms. In the same 

 way Duvau subsequently followed the course of eleven genera- 

 tions ; whilst Kyber, by keeping a colony of the insects in a 

 warm room, continued this process of virgin reproduction for no 

 less than four years. 



It is no wonder that circumstances so truly remarkable should 

 have excited great attention amongst naturalists, or that various 

 theories should have been advanced to account for it. Reaumur 

 indeed endeavoured to elude the difficulty altogether by assert- 

 ing that Aphides were androgynous ; while Leon Dufour referred 

 the phenomena to spontaneous or equivocal generation. The 

 true explanation in all probability is that suggested by Steen- 

 strup, who gives the reproductive virgins the curious name of 

 ammen, or wet-nurses, and treats the matter as a case of " alterna- 

 tion of generations." It is quite clear, however, that much has 

 yet to be done before the matter can be regarded as settled, and 

 any enterprising entomologist may, if he will, turn to good 

 account the little vermin which batten on his geraniums and 

 calceolarias, by still farther following up the subject. 



Closely connected, and in many respects, no doubt, identical, 

 with this anomalous mode of reproduction among the Aphides, is 

 the phenomenon which has been designated parthenogenesis, or re- 

 production by virgins, which are indisputably true females. Pro- 

 fessor Siebold, of Berlin, has greatly added to our knowledge of 

 the insect wonders of this kind by his essay " Ou a True Parthe- 

 nogenesis in Moths and Bees," a work which has been given to 

 the English public in a translation by Mr. Dallas, one of our 



