132 BRITISH APHIDES. 



Afterwards other winged specimens were examined, 

 some of which appeared to be quite barren, but others 

 contained variable numbers of foetus, from a single 

 example up to twelve. On another occasion two black 

 females were seated on the same leaf, and the imme- 

 diate proximity of a dozen pseudomorphs led again to 

 the inference that they were the corresponding off- 

 spring of these females. 



Signoret describes another form of Aphis feeding on 

 the maple, to which he gives the name Aphis perforatiis, 

 chiefly from the occurrence of tubercles or punctures on 

 the third and fourth antennal joints. I suggest that 

 such slight differences are due to their being indivi- 

 duals of a later brood, for such specimens often 

 approach the characters of the winged adult. The 

 presence of such tubercles is common in Siphono- 

 phora and other genera. 



What is the significance of this particular phase in 

 the economy of Chaitophorus ? Their appearance on 

 the leaves many months before the oviparous females 

 come into existence precludes all idea that they 

 are males. Landois and others have shown that 

 sexual development in insects, as in other animals, is 

 closely connected with conditions of alimentation, and 

 perhaps larval forms are peculiarly, in this respect, 

 plastic. The sexual development of the queen of the 

 honeybee is a familiar case in point. 



But in Gil. aceris the phenomenon can scarcely be 

 considered as an arrest of development through 

 deficient food, for it has been shown that the perfect 

 sexes may be bred at the same time on the same leaf. 

 If the fact be certain that the same individual produces 

 the two forms simultaneously, the interesting subject 

 invites closer attention than has yet been bestowed 

 upon it. 



In searching for analogies to the facts above, the 

 mind naturally reverts to the discovery recently made 

 known, that the larva3 of certain Tijjulidce have powers 



