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



be lengthened by art, would in time wear out the species, as the 

 skin-shedding or the change of form (both which acts seem to 

 typify or to resemble the first- mentioned process) tends to exhaust 

 the insect, were not such a casualty provided for by the appear- 

 ance of the second form after the lapse of a few generations of 

 the winged female. 



2. The oviparous wingless female. 



The viviparous Aphides produce oviparous females and males 

 at different times of the year, but in most species the first ap- 

 pearance of the two latter forms is autumnal. The law which 

 thus ordains an alteration of form may be compared to that which 

 adjusts the relative proportions of the foliage, flowers, and seeds 

 of plants to the conditions of the soil and of the atmosphere ; and 

 these two agents bear the same relation to vegetation as the lat- 

 ter does to Aphides with respect to inducing a change of structure. 



3. The winged male, 



whose appearance in the two following species precedes the fall 

 of the leaf where it dwells, and then its partner, the oviparous 

 female, lays the eggs which by their glutinous covering are fast- 

 ened to the twigs, and thereby secured from injury during the 

 winter till the first mild weather in the spring recalls the species 

 to active life. 



1. Aphis Platanoidis. 



Aphis Platanoidis, Schrank, Fauna Boica, ii. 1. 112; Kalten- 

 bach, Mon. Pfian. i. 13 ; Ratzcburg, Forst. Ins. iii. 216. 1. 11. f. 4; 

 Hartig, Germ. Zeit. iii. 309. 



Aphis Pseudo-platani, Sir Oswald Mosley, Gardener's Chro- 

 nicle, i. 684. 



It feeds on Acer Pseudo-platanus, the sycamore; A. Plata- 

 noides, the plantain-like or Norway maple; and sometimes on A. 

 campestre, the field maple, and is stationed on the under side of 

 the leaf. 



The viviparous winged female. This is hatched from the egg- 

 in February or in March, and while young or a pupa it is slender, 

 pale green, rather flat and hairy, and adorned along the back with 

 four rows of black dots, with two vivid green stripes, and with 

 two rows of projections, which are separated by three rows of 

 smaller tubercles ; these and the hairs diminish or disappear du- 

 ring the growth of the insect : the limbs are dull green : the 

 feelers are stout, and rather shoi'ter than the body ; their joints 

 have black tips : the eyes are black : the tip of the mouth is 

 brown : the nectaries in the very young insect are not more than 

 one-twelfth of the length of the body : the legs are short and 

 stout. 



