418 Transactions. — Zoology. 



may be distinguished from the "late larva" principally by its 

 size. But it happens not unfrequently that there are other 

 characters which may be employed. Colour may be to some 

 extent considered, and in many cases the pupae can be recog- 

 nised by their darker tinge. As a rule, also, the rudimentary 

 feet and antennae are in this stage much more distinctly 

 visible, although sometimes (e.g., A. barodensis, A. limhata, 

 &c.) the very dark colour prevents this. Again, sometimes 

 the fringes or hairs of the larva are absent from the pupa 

 {e.g., A. asplenii, A. cotcsii), or the arrangement of the hairs 

 or w-ax may differ {e.g., A. hirsuta). On the whole, it is not 

 difficult to decide whether a specimen is a larva or a pupa, 

 though there are exceptions; of course, there can be no doubt 

 in those cases where the larval exuviae are seen on the dorsum 

 of the pupa. 



I may here remark, in passing, that, as far as my experience 

 goes, the Aleurodidce differ from other Homoptera in being 

 always on the under-surface of leaves. Coccidcs and PsijllidcB 

 are found indiscriminately on leaves or twigs, and often on 

 both upper and lower surfaces of a leaf; but I have never seen 

 an Aleurodes except on a leaf, on the lower side — -I mean, of 

 course, a larva or a pupa. 



It remains to speak of an organ which is quite charac- 

 teristic of this family, and which, more or less modified, is 

 visible in every stage of growth after the egg. Viewing an 

 Aleurodid larva or pupa with the naked eye, or with a lens of 

 low magnifying-power, it is scarcely possible to distinguish it 

 from a Coccid, especially of the section Lccanince, especially if, 

 as sometimes happens {e.g., A. dccipiens), there is a cleft in the 

 abdominal extremity. But on applying a greater magnifying- 

 power it is observed that, whereas in a Lecanid there are two 

 minute subconical lobes visible on the abdominal dorsum, 

 tliere is seen in an Aleurodid a minute orifice, more or less 

 elliptical or subconical posteriorly, and more or less depressed, 

 or even slightly convex, anteriorly. This orifice is partially 

 closed by a plate which is hinged on the anterior edge of the 

 orifice, but does not extend altogether to the posterior edge. 

 No author known to me has entered into any details regarding 

 this organ ; and yet, as it is persistent in one form or another 

 from the earliest larval stage to the latest adult state, and is 

 entirely characteristic of the family, it may be well to eluci- 

 date it as far as possible. Signoret merely remarks that in 

 the adult there is on the last abdominal segment "a kind of 

 elongated tubercle of varying shape, apparently allied to the 

 cornicles of ^^/ws " ; but he does not say anything about its 

 presence in the earlier stages. I have not found any other 

 author who pays particular attention to this organ except Mr. 

 E. T. Lewis (Journ. of Quekett Micr. Club, 1895), who 



