Insects. 2003 



themselves so exceedingly curious, and at the same time are so unexplained by any 

 hitherto received theory of generation deduced from observations on vertebrated ani- 

 mals, that I have been desirous of verifying these facts by direct experiment, prepara- 

 tory to attempting hereafter to show their accordance with some universal law of re- 

 production. I trust, therefore, that I may now be permitted in this short note to bear 

 testimony to the correctness of the observations of Leeuwenhoek, Bonnet and Reau- 

 mur, on the mode of generation in the Aphides, although at present I can add but lit- 

 tle to what has already been observed by those naturalists. The facts T have more 

 particularly endeavoured to investigate, are — first, whether the Aphis is in reality vivi- 

 parous at one season, and oviparous at another ? and next, whether the supposed ova 

 are deposited as true eggs ; or whether, as imagined by some observers, they are only 

 capsules designed to protect the already formed embryos during the winter season ? 

 With these objects in view, I selected the Aphis of the rose, as best fitted for the en- 

 quiry. 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 co- 

 vered with Aphides, amongst which I had not yet seen any winged specimens ; neither 

 had any of the females yet deposited ova. The rose tree was placed in the window of 

 an apartment in which there was no fire, and where the temperature ranged from 

 about 45° Fahr. to 50° Fahr. In the second week of November, as the temperature of 

 the season became cooler, I first noticed several specimens with rudiments of wings, 

 and a few days afterwards these cast their skins and became fully developed. Most 

 of these individuals were males. At this time there were also a great many very young 

 specimens. On the 30th of November the number of winged individuals had greatly 

 increased ; there were many with only the rudiments of wings : and there was also a 

 great abundance of black oval eggs distributed everywhere on the young shoots of the 

 plant, not only on the leaf-buds, but on the stems of the leaves and branches. I saw 

 an Aphis at that moment bearing two eggs at the extremity of her body. On placing 

 one of these beneath the microscope, I was quickly assured of its real nature : it was 

 not a capsule that included a ready-formed embryo, but a true egg. When first de- 

 posited the egg is of an orange-yellow colour, but it soon acquires a much darker hue, 

 and ultimately becomes of a deep shining black. The colour is entirely dependant 

 on the pigment of the shell, and is much darker in some specimens than in others. 

 The eggs are firmly glued to the plant, and are not easily removed. The egg of the 

 Aphis is similar to that of other insects ; it is composed of an orange-coloured yelk, 

 formed of yellow nucleated cells, and surrounded by a very slight quantity of transpa- 

 rent vitelline fluid. It contains also a very large germinal vesicle, with a distinct ma- 

 cula or nucleus. This vesicle is three or four times as large as the cells that compose 

 the yelk, and, unlike that of most other impregnated eggs of insects, does not disap- 

 pear until some time after the egg is deposited. The vesicle is so persistent, that in 

 one instance in which I examined an egg, shortly after it came from the body of the 

 Aphis, it did not disappear for several seconds after the egg was crushed under the 

 microscope. 



" Wishing to observe the deposition of more eggs, I selected four specimens of the 

 Aphis for experiment : two of these were males, which as yet were in the pupa state, 

 and had only the rudiments of wings ; the other two were large apterous females : 

 these were placed on a detached branch of the rose, inclosed in a stoppered glass ves- 

 sel, and removed to an apartment, in which the temperature ranged from 55° Fahr. to 

 about 60° Fahr. On the 2nd of December, when the temperature of the room was 



