STATE HORTICULTURAL SOCIETY. 



149 



middle third of the rib-vein arise three branches, which run obliquely- 

 outward to the hind margin of the wing ; the outer, or third branch, 

 gives off from its posterior side two branches, or in other words, forks 



F.g.I 



Fiq.m 



Fig.lT. 



Fig.W '^^^ 



Fig.VM 



Fig. 3. 



I. Aphis maidis — winged insect. 



II. Head and antennae of Aphis avencB. 



III. Aphis maidis — wingless female. 



IV. Portion of corn root infested liy A. maidis. 



V. The/axes ulmicola — showing veins of wings and antenna;. 



VI. Pemphigus populicaidis — showing veins of wings and antenn.'«. 



VII. (Should be omitted.) 



\'III. Wings of Phylloxera. 



twice. (Fig. 3, No. I.) In some species the third vein forks but once, 

 (Fig. 3, No. V. ;) in others it is simple, without any branches, (Fig. 3, 

 No. VI. ;) in others the third branch is almost or quite obsolete, (Fig. 3, 

 No. VIII. ;) each variation corresponding with some important difference 

 in the anatomy or habits of the species. It is therefore on account of the 

 material differences in the characters and habits of the species which 

 these variations of the wings indicate that they are selected as a means 

 of classifying and describing these insects, and not that the absence or 

 presence of a single veinlet is considered important in itself. 



The hind wings, which are generally (though not always) much 

 smaller than the fore wings, in the typical species have the chief or rib- 

 vein close to the front border, giving off two branches on the posterior 

 side ; sometimes there is but one. These branches, both in the fore and 

 hind wings, are usually termed the discoidal veins, in order to save a long 

 description by which to identify them. The chief difficulty in using the 

 wing-characters arises from the fact that the very large majority of the 

 individuals we see are without these organs, and do not acquire them 

 during life; yet, as will be seen hereafter, there are few, if any, species 



