STATE HORTICULTURAL SOCIETY. 139 



fouiid more or less covered with a whitish cottony or downy substance, 

 while others are always naked ; some possess little horn-like appendages, 

 called "honey tubes," arising from the upper part of the abdomen near 

 the tip, while others are entirely without these; some have the very sin- 

 gular habit of bringing forth their young alive, while others are always 

 oviparous ; some confine their operations exclusively to the leaves, others 

 to the twigs and bark, and others to the roots, while others operate both 

 on the stem and root or leaves and roots ; some reside exposed on the 

 surface of the leaves or bark, while others, by some peculiar power, not 

 yet well understood, form galls in which they carry on their operations 

 and pass the greater portion of their existence ; in most cases the pupce 

 are active as the perfect insects, yet there are some species in which these 

 are stationary, and resemble the apparently lifeless scale of the Bark-lice. 



Most of the species, at some period of the year, present winged 

 individuals of one or both sexes, yet their habits in this respect are widely 

 different, and the differences between the wings of the different species 

 afford some of the best characters yet observed for separating them into 

 generic or larger groups. For example : In a very large portion, in fact 

 in most of our American species, the wings are very thin and membra- 

 neous and almost perfectly transparent, while in one very singular group 

 they are opaque and more or less covered with a fine powder, giving them 

 the appearance of minute moths. Very marked differences are found in 

 the veining of the transparent wings of the former; in some the rib-vein 

 or chief vein of the forewings is central, and as it proceeds toward the 

 apex divides into branches, each of which is again divided ; while in 

 another very large group the rib-vein coasts along near the front margin, 

 giving off on the posterior or inner side three branches which run 

 obliquely outward and backward to the hind margin ; some have the 

 third or outer branch twice forked, others once, while in others it is simple 

 or unbranched. Some species place their wings, when in repose, 'against 

 each other, above the back, in the form of a very steep roof, while 

 others rest them horizontally on the abdomen. Some have the antennae 

 as long or even longer than the body, while in others these organs do not 

 reach the middle of the thorax ; these organs, when tipped with two 

 bristles, are usually stem or nine-jointed, while in all other cases they are 

 but seven or less than seven-jointed. 



Some of these differences will doubtless be considered unworthy of 

 notice by those who have never devoted any time to the study of insects 

 and their characters ; but when it is found by close and persistent study 

 of the habits of these insects that the difference in the number of forks 

 in one of the branch or discoidal veins is always accompanied by a marked 

 difference in habits, this character, although apparently insignificant, is 

 really important. A knowledge of these facts enables the entomologist, 

 if he can see but a single tiny forewing, to tell at once to what group the 

 species belongs and what are its habits. 



Notwithstanding these differences between the groups and species, 

 there are certain characters in which all agree, the more important of 

 which are as follows: 



