100 MISS EMBl.ETOK ON CEEATArillS LATAKIJ-:. 



History * Dr. Sharp saj-s : — " The simple form of Aphid h"fo nmy 

 be described as follows : — Eggs are laid iu the autumn and 

 hatch in the spring, giving rise to females of au imperfect 

 character having no ^Yings ; these produce living young partheno- 

 genetically, and this process may be repeated lor a few or for 

 many generations, and there may be in these generations a greater 

 or less number of winged individuals, and perhaps a few males. 

 After a time when temperature falls, or when the supply of food 

 is less in quantity, or after a period of deliberate abstention from 

 food, sexual individuals are produced, and fertilized eggs are laid 

 which hatch in the spring, and the phenomena are repeated. In 

 other cases these phenomena are added to or rendered more 

 complicated by the intercalated parthenogenetic generations 

 exhibiting well-marked metamorphosis, of kinds such as occur in 

 apterous or winged insects ; while again the habits of successive 

 generations maj- differ greatly, the individuals of some genera- 

 tions dwelling iu galls, while those of other generations live 

 underground on roots." 



It being taken for granted that Cerataplds lafanicv as found 

 in Britain is an Aphid, although it departs biologically very 

 ■widely from that group of Insects, inasmuch as it appears to be 

 totally deprived of those successiomil metamorphoses that are 

 so characteristic of Ajpliidcc, it becomes iuterestirg to inquire 

 how this arises. Iu oi'der to make my ideas on this point 

 comprehensible it is advisable briefly to summarize Pergande's t 

 receut remarkable discoveries as to the life-histories of migratory 

 Aphides. Although the results are only lately published, he has 

 been prosecuting this inquiry for more than 20 years. The 

 simplest form of Aphid-life is tliat described by Dr. Sharp, and 

 quoted above, while the most complex is that described by 

 Pergande. He shows that these migratory Aphides exhibit the 

 most complex form, not merely of ontogenesis, but also of the 

 cycles of generations that are so marvellous in this family. He 

 has discovered that these creatures possess, iu their ontogeny, an 

 '' aleurodiforni " stage, to which our hothouse inhabitant bears 

 a most striking resemblance. The allied forms which Pergande 

 studied are Sormaphis Jianiamelidis, Pitch, and Hai?iamelistes 



* Insects, part ii. p. 582. 



t U.S. Dep. Agric, Eut. 1901, no. 9. '• The Lile-histoi-y of two Species of 

 Plant-lice, inhabitino; both the Witch-hazel and Bii-cli." 



