SCIENTIFIC SURVEY. 



201 



anomalous way of increase of individuals as a process of bud- 

 ding, and that the whole series, like the leaves of a tree, con- 

 stitutes but a single generation, which results from the union 

 of the sexes in the previous fall. It has always been supposed 

 that the final autumnal set of individuals were males and females 

 alone. Hear Dr. Burnett again : " The terminal brood has hither- 

 to been considered, as far as I am aware, to be composed exclu- 

 sively of males and females, or, in other words, of perfect insects 

 of both sexes. I was surprised therefore on examining the in- 

 ternal organs of the non-winged individuals, to find that many of 

 these last were not females proper, but simply the ordinary gem- 

 miperous form. Moreover so great was the similarity of appear- 

 ance between these two forms — true females and gemmiperous 

 individuals — that they could be distinguished only by an examina- 

 tion of their internal genitalia." 



Aphides, (Fig. 26,) are found upon every part of ^'°- ^^■ 



plants. Some species which are wingless, are ( ^^r^ 

 found on the roots of plants, others on the stems 

 or twigs, others roll up leaves, or form gall-like swellings on 

 leaves ; the grain aphis sucks the sap of the kernel. Ants are 

 fond of the sweet excretions from the abdominal stylets, and 

 often keep them captives in their nests like herds of cattle. Syrphus 

 flies, and Coccinellae, keep them within proper limits in nature. 

 Minute species of Aphidius, small Ichneumons, kill larger numbers 

 than we imagine. " When an aphis has received an egg from one 

 of these parasites, it quits its companions and fastens itself by its 

 ungues to the under side of a leaf, when it swells into a globular 

 form, its skin stretched out and dried up, and in a short time the 

 perfect parasite escapes by a circular hole, the mouth of which 

 sometimes remains like a trap door." 



Eriosoma lanigerum, the American blight, a wooly or cottony cov- 

 ered species, feed on the sap wood of the apple. 



Coccidae, or bark lice, are scale-like in form like miniature oyster 

 shells, and live on the bark of trees, or upon the roots. The males 

 alone are winged and pass through the usual changes, while the fe- 

 male only increases in size, preserving its scale like form. "Early in 

 spring the bark lice are found apparently torpid, situated longitud- 

 inally in regard to the branch, the head upwards, and sticking by 

 their flattened inferior surface closely to the bark. On attempting 

 to remove them they are generally crushed, and there issues from 



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