THE CABBAGE APHIS. 167 



has been called by Professor Owen, of London, 'Partheno- 

 genesis.' Various experiments have been made by some 

 naturalists to observe the transformation of the aphides, 

 and to test the accuracy of their first impressions concern- 

 ing their propagation. Barjin found that the aphides of 

 the rose and poppy produced young without having paired. 

 The experiments of Bonnet, as already mentioned in a 

 previous chapter of this part of the book, are particularly 

 interesting. He watched for the production of a young 

 aphis from a mother without wings, that is from a fertile 

 pupa ; he then placed it on a leafy branch of the plant to 

 which it belonged, having first ascertained that the twig 

 selected was totally free from blight. He then fixed the 

 branch with the insect in a glass tube inserted in a pot of 

 garden mould, so covered over with a bell-glass as to 

 prevent the possibility of any intrusion. The single in- 

 sect was thus completely isolated, but provided with means 

 of life. He then carefully watched his young nursling, 

 and examined it at short intervals of time with a lens. 

 He found that it gradually increased in size, and by the 

 time that it had attained its full dimensions had changed 

 its skin no less than four times. On the twelfth day of its 

 imprisonment it produced a living duplicate of itself, and 

 in the three weeks following brought forth no fewer than 

 95 young ones. Bonnet afterwards found that from nine 

 to eleven generations were produced without pairing, 

 and his observations were confirmed by the experiments 

 of Lyonnet and Duvan. 



" A single female (using the last word single in both 

 senses) might thus in one season be the parent of the 

 astonishing number of a hundred and fifty millions, 

 assuming the descent to consist of nine generations, and 

 each individual to have eight in family, and all to do well. 

 For the first family will number eight ; the second eight 

 times eight, plus the former ; the third eight times eight 

 times eight, with the same addition ; and so on until 

 figures refuse to express the result and the mind fails to 

 form an idea of the vast multitude. About the ninth or 

 tenth generation this remarkable fecundity becomes 



