Mr. F. Walker's Descriptions of Aphides. 191 



sects ; many of them have so much mutual resemblance that they 

 are easily confounded together under one name, and a single plant 

 is often the food of several, and in some instances of nine differ- 

 ent kinds ; but on the other hand, their migrations from one plant 

 to another have occasioned the number of the names to exceed 

 that of the species. The winged and wingless forms are usually 

 alternate with each other ; the latter proceeds from the egg in the 

 spring, and its descendants are winged, and thereby enabled to 

 migrate to other plants where they have a wingless offspring, and 

 these successive generations most often continue till the autumn, 

 when the male and the oviparous female appear. This group will 

 form several subgroups, and Aphis Rosce, A. Sonchi, A. Absin- 

 thiiy and A. Millefolii may be included in one of these lesser 

 divisions ; these species are of the largest size, and possess the 

 full development of the peculiar structure of their tribe, such 

 as the shape of the head, of the nectaries, and of the tip of the 

 abdomen, which characters are more or less modified in most of 

 the following species. I take this opportunity of inserting a 

 translation of Kaltenbach's divisions of Aphides, with a list of 

 the species described by him. 



A. Seventh feeler-joint bristle-shaped and longer than the 

 sixth. 



a. The feelers seated on tubercles of the forehead. 



*. Forehead deeply groove-shaped. 



a. The wingless insects green. 



1. Rosse. 4. Urticae. 7. Hieracii. 10. Pelargonii. 



2. Millefolii. 5. Sdlani. 8. Tanacetaria. 11. Pisi. 



3. Platanoides. 6. Cerealis. 9. Viciae. 12. Rubi. 



/3. The wingless insects brown or red. 



13. Serratulae. 17. Sonchi. 20. Solidagmis. 



14. Campanula. 18. Taraxaci. 21. Tanaceticola. 



15. Jaceae. 19. Absinthii. 22. Ribicola. 



16. Picridis. 



**. Forehead flat or arched. 



23. Galeopsidis. 29. Dianthi. 34. Ligustri. 



24. Humuli. 30. Betulicola. 35. Lonicerse. 



25. Lactucae. 31. Cerasi. 36. Lythri. 



26. Ribis. 32. Aparines. 37. Pruni. 



27. Convolvuli. 33. Tanaceti. 38. Arundinis. 



28. Chelidonii. 



b. Feelers seated immediately on the forehead which is flat or 

 convex. 



*. Body oval, highly arched, with a little tubercle on each side 

 of the last but one abdominal segment. 



39. Urticaria. 42. Scabiosae. 45. Rhamni. * 



40. Capsellae. 43. Sympbiti. 46. Epilobii. 



41. Plantaginis. 44. Sedi. 47. Cratsegi. 



