Maskell. — On Aleurodidffi. 419 



mentions it, and gives figures of it on the adult only ; and Mr. 

 J. W. Douglas, wlio, in the Entomologists Monthly Magazine, 

 1891, figures the organ on the pupa of A. ruhicola. 



I have in this paper noted carefully what seem to be 

 specific variations in this organ, believing it to be quite a valid 

 differentiating character. It consists of three parts. First, 

 an orifice in the dorsal surface of the abdominal region, to 

 which I have given the name of the " vasiform orifice," 

 from its general outline. Secondly, a plate hinged upon the 

 anterior edge of the orifice, which I call the " operculuiai," 

 and which does not entirely cover the orifice. Thirdly, a 

 more or less slender, subcylindrical, tongue-like tube, which I 

 call the "lingula," and of which the length varies consider- 

 ably, being sometimes shorter than the operculum {A.fodiens), 

 sometimes very much longer {A. decipiens). In the adult 

 stage the lingula, as a rule, does not project when at rest, the 

 w^hole organ then appearing as a simple open tubercle on the 

 abdominal dorsum; but in some species {e.g., A. asparagi, 

 and in all probability A. decipiens) it protrudes as a con- 

 spicuous cylindrical tongue. The lingula also very frequently 

 bears some fine hairs or setse, varvins from extremelv minute 

 to considerably long ones. 



I strongly incline to the belief that this organ is con- 

 cerned with the secretion of "houeydew." The AleurodidcB 

 do not seem to produce this substance in such quantities as 

 the Coccidce and the Aphididce, and the leaves which they 

 attack are therefore usually less subject to be covered with 

 black fungus than is the case with those families ; but they do 

 produce some. For example, Messrs. Kiley and Howard, in 

 Insect Life, 1893, p. 316, observe of A. cocois, "The upper 

 surface (of a leaf) is frequently attacked by a smut-fungus 

 which is developed on the honeydew thrown down from 

 the under-sides of the leaves above. The honeydew attracts 

 numerous ants." In my paper " On the Honeydew of Coccida 

 and the Fungus accompanying these Insects" (Trans. N.Z. 

 Inst., 1886, p. 41), I drew special attention to this secretion 

 and to the blackening of the leaves by it, and I described and 

 figured an organ which I had actually seen employed in the 

 production of honeydew in the species Gtenochiton elceocarpi. 

 That species belongs to the Coccid section Lecanince, and in 

 that section, on the abdoininal dorsum, there are always pre- 

 sent two subtriangular projecting lobes, from between and 

 beneath which the tubular organ just mentioned was pro- 

 truded whilst I was watching the specimen. I am convinced 

 that the "lingula" of Aleurodes is homologous with the 

 honeydew organ of Gtenochiton, and that its function is the 

 production of honeydew. 



In a letter to me respecting A. asparagi Mr. Lewis tells 



