XXXI 



ON THE PHENOMENA OF GEMMATION 



Abstract of a Friday Evening Discourse at the Royal Institution, May 21, 

 1858; Roy. Inst. Proc. vol. ii. 1854-58, //. 534-538; Silliman, Journ. 

 xxviii., 1859, //. 2o6-2og 



The speaker commenced by stating that a learned French 

 naturalist, M. Duvau, proposed many years ago, to term the middle 

 ■oi the eighteenth century, " TEpoque des Pucerons ; " and that the 

 importance of the phenomena which were first brought to h'ght by the 

 study of these remarkable insects renders the phrase " Epoch of 

 Plant-lice," as applied to this period, far less whimsically inappropriate 

 than it might at first sight seem to be. 



After a brief sketch of the mode of life of these Plant-lice, or 

 Aphides, as they are technically termed ; of the structure of their 

 singular piercing and sucking mouths ; and of their relations to what 

 are called " Blights ; " the circumstances which have more particularly 

 drawn the attention of naturalists to these insects were fully detailed. 



It was between the years 1740 and 1750, in fact, that Bonnet, 

 acting upon the suggestions of the illustrious Reaumur, isolated an 

 Aphis immediately after its birth, and proved to demonstration, that 

 not only was it capable of spontaneously bringing forth numerous 

 living young, but that these and their descendants, to the ninth 

 generation, preserved a similar faculty. 



Observations so remarkable were not likely to pass unheeded ; 

 but notwithstanding the careful sifting which they have received, 

 Bonnet's results have never been questioned. On the contrary, not 

 only have Lyonet, Degeer, Kyber, Duvau, and others, borne ample 

 testimony to their accuracy, but it has been shown that, under 

 favourable conditions of temperature and food, there is practically 

 no limit to this power of asexual multiplication, or as it has been 

 ■conveniently termed, " Agamogenesis." 



Thus Kyber bred the viviparous Aphis Dianthi and Aphis Roses 



Y 



