I04 Annals Entomological Society of America [Vol.11, 



tion except that even the balsam mounts remained usable for a 

 sufficient time to secure camera lucida drawings of the points in 

 question. In preparations for photomicrographs the glycerine 

 jelly mounts were better. 



After comparing the two methods the balsam mounts were 

 used almost altogether as they were quicker and simpler to pre- 

 pare and a much larger proportion of usable mounts w^ere made 

 in this way. 



The wings of freshly emerged aphids were severed from the 

 body together with a portion of the thorax, to preserve the basal 

 part of the tracheae and to block to some extent the penetration 

 of the balsam. 



In some species, where the shape of the body and the angle at 

 which the wings are set permitted it, the aphid itself with wings 

 attached was mounted after beheading the insect and puncturing 

 the tip of the abdomen. The legs had also to be removed. The 

 pressure of the cover glass in these mounts generally forced the 

 body fluids from the openings at the tw^o extremities and often 

 excellent tracheal preparations w^ere secured in this way. It 

 could be applied only to a limited number of species, however. 



Only wings of freshly emerged aphids are available for the 

 study of the wing tracheae, as before the wings are hardened 

 enough for the first flight, the tracheae have become either en- 

 tirely invisible or so nearly so that they are useless for the ques- 

 tions in hand. It thus becomes necessary to select the individuals 

 ■ in the first few minutes after molting. This can readily be done 

 by taking the palest insects while the wings are yet white, that is, 

 before they begin to become transparent. An abundance of 

 material was kept on hand by the collection of large colonies of 

 aphids whenever any were found, the wing pads of which indi- 

 cated that the final molt was approaching. 



It was more difficult to secure the wing pads at the critical 

 moment. The wing pad of the aphid nymph is not only small 

 but it is relatively thicker and softer and narrower than those of 

 many insects and the developing wing is for the most part so 

 crumpled that the courses of the tracheae are impossible to follow. 

 So soft is the tissue of the nymphal pad and so loose do the tra- 

 cheae lie within it, that the slighest pressure is likely to misplace 

 them or rupture them, and render the preparation useless. By 

 selecting the nymphs of such species as had the flatter wing pads. 



