250 Mr. F. Walker’s Descriptions of Aphides. 
be lengthened by art, would in time wear out the speeies, 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 wunged 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. Pflan. i. 13 ; Ratzeburg, Forst. Ins. iii. 216. 1. 11. f. 4; 
Hartig, Germ. Zeit. iii. 369. 
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 shorter 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. 
