142 BRITISH APHIDES. 



ties by the influence of the male sperm-elements, and 

 proceed to develop as females.* 



Mr. Darwin suggests that the union of individuals 

 has the effect of fusing two life-experiences in the pro- 

 geny, which thus obtains other and wider tendencies 

 and impulses. Thus self-impregnation and partheno- 

 genesis would have to yield to the more active and 

 developing process of di-genesis, that is to say, of the 

 concurrence of two individuals. 



E. Witlaczil f has recently made observations on the 

 general reproductive anatomy of Aphides. In the 

 same paper he describes the fat secreting body, which 

 is largely developed in the abdomen of these insects. 

 It has been before noted by me that the oil globules, 

 secreted as minute drops from the above tissue,' take 

 various tints, such as pink, green, yellow, or red ; and 

 that the coloration of certain species of Aphis is due 

 to their presence. 



The above-mentioned author discusses the muscular 

 system of these insects, and he divides the same into 

 a motor and respiratory grouping ; such being respec- 

 tively distributed cither to various parts of the abdo- 

 men or to the tracheae and the stigmata. The cephalic 

 ganglia arc connected with the eyes, antennae, and 

 oesophagus ; and marks are made in the memoir on 

 the pits in the antenna?, which are here referred, not 

 to organs connected with hearing, but to those of 

 smelling. The antennae would seem to serve, he 

 thinks, not so much for finding the female as for 

 discovering suitable food. 



"O 



The wax-glands (silk ?) which I have before des- 

 cribed as present in Chermcs dbietis (vide vol. i, PI. C, 

 fig. 6) he finds also to be present in Pemphigus bur- 

 sarins. This species has four on the pro-thorax, six 

 on the meso- ;md meta-thorax and the first six 



* Von Siebold, ' Comp. Anat.,' transl. by Dr. Burnett. Also vide 

 ' Nature.' October 24th, 1872, p. 523 ; notes by Prof. E. Ray Lankester. 



f E. "Withicz.il, ' Arbeit. Zool. Ins. Wien,' iv (1882), pp. 397—441 

 (2 pis). Abstract, ' Quart. Journ. Mic. Sc.,' ser. 2, vol. iii, p. 40. 



