68 HOP-FLY. 



and yet continues to increase in size all the while ; there 

 seem to be no males, no drones, all bring forth alike.* 



* The study of this obscure tribe of insects has not been attended with any 

 great success, neither has it enabled us to arrive at very positive conclusions 

 concerning this apparently anomalous mode of reproduction. Some authors 

 assert that the same individual female at one period of her life produces living 

 young and at another period is truly oviparous : others contend that the ovipa- 

 rous and viviparous females are perfectly and constantly distinct; indeed Mr. 

 Walker goes so far as to describe six different kinds of individuals of the same 

 species, viz., 1, a winged oviparous female; 2, a wingless oviparous female ; 3, 

 a winged viviparous female ; 4, a wingless viviparous female ; 5, a winged 

 male ; 6, a wingless male. My own observations, interrupted and incomplete 

 though they be, tend to favour the view evidently entertained by our author, 

 that the wingless female is the parent of the winged female, and that the latter 

 is generally oviparous, while the former is generally viviparous : exceptions cer- 

 tainly occur. On the other hand, I have never met with an instance in which 

 an oviparous individual became viviparous, or vice versa : but in support of 

 such a fact I will quote from the ' Zoologist' (Zool. 2002) an able paper re- 

 cently published by Mr. Newport. E. N. " The history of the plant-louse, as 

 ascertained by Leeuwenhoek, Bonnet, Reaumur, and others, is so generally 

 known to naturalists, that it is almost an act of supererogation for any one merely 

 to repeat the observations of those authorities; and we cannot expect to add much 

 to the very ample details they have given : yet the facts they have recorded re- 

 specting the generation of Aphides are in themselves so exceedingly curious, 

 and at the same time are so unexplained by any hitherto received theory of ge- 

 neration deduced from observations on vertebrated animals, that I have been 

 desirous of verifying these facts by direct experiment, preparatory to attempting 

 hereafter to show their accordance with some universal law of reproduction. I 

 trust, therefore, that I may now Le permitted in this short note to bear testi- 

 mony to the correctness of the observations of Leeuwer.hoek, Bonnet and Reau- 

 mur, on the mode of generation iu the Aphides, although at present I can add 

 but little to what has already been observed by those naturalists. The facts 

 I have more particularly endeavoured to investigate, are first, whether the 

 Aphis is in reality viviparous at one season, and oviparous at another ? and 

 next, whether the supposed ova are deposited as true eggs; or whether, as ima- 

 gined by some observers, they are only capsules designed to protect the already 

 formed embryos during the winter season ? With these objects in view, I se- 

 lected the Aphis of the rose, as best fitted for the inquiry. In the beginning of 

 November, 1842, the young shoots of a rose tree, that had remained in the open 

 air during the whole of the preceding summer, were thickly covered with Aphi- 

 des, amongst which I had not yet seen any winged specimens ; neither had 



