1889.] 191 



among the Aspidioti, there are A. rapax (= or closely allied to A. 

 camellias), A. perniciosus, A. aurantii, A. tenehricosus, all of which are 

 without these glands, and yet they spin scales almost precisely similar 

 to those spun by species such as A. nerii, A. convexus, &c, which are 

 provided with four groups. Indeed, Comstock mentions (p. 295) that 

 "A. convexus very closely resembles A. rapax in the shape and colour 

 of its scale." He says, " the resemblance of the two species is so 

 great, that at first I considered them identical." But it must be re- 

 membered that some species secrete what Prof. Comstock (p. 281) 

 terms a ventral scale, indeed, in all instances that I am aware of, as 

 Dr. Witlaczil also remarks (p. 159), a white, thin, slimy -looking film 

 will generally be found remaining on the plant after the insect is 

 removed, although I do not think this can be considered analogous to 

 the true filamentary dorsal scale, for it more resembles a stain where 

 the insect has been fixed, being of its precise shape and size. Some- 

 times, however, the insect is enclosed in what Comstock terms an 

 "entire" ventral scale, which, however, appears to consist in a great 

 measure (as he suggests) of the ventral half of the rejected larval 

 skin. In any case, these "ventral grouped glands" do not seem to 

 have any relation to the ventral scale, because, for instance, both the 

 species A. rapax and A. aurantii have well developed " entire " ventral 

 scales, and yet they have no grouped ventral glands ; whilst, on the 

 other hand, A. nerii has four groups of ventral glands, and yet has no 

 ventral scale, except the white film before referred to. I should now 

 mention that these groups of ventral glands are never found on the 

 male, and as a rule on the female only when it has arrived at maturity. 

 I have occasionally, but very exceptionally, found them on an imma- 

 tured female. Having been termed by authors " spinnerets," they 

 have been considered as analogous to the dorsal spinnerets found on 

 the lateral margins of the dorsal segments of both sexes of some spe- 

 cies of the Coccina sub-family, e. g., Dactylopius cyperi, described by 

 Dr. Signoret (p. 348), and in Dactylopius citri, as shown in fig. 4, but 

 these, as I have before mentioned, are true dorsal spinnerets, and 

 cannot, I think, be correctly compared with the ventral grouped glands 

 now under consideration. To find organs analogous to these in the 

 Coccina and Lecanina, a close examination must be made towards the 

 ventral surface in the adult female, in the neighbourhood of the ano- 

 genital organs, and in the species Lecanium olece for instance, there 

 will be found glandular organs such as are shown in fig. 6, v. s. g., 

 likewise in Dactylopius citri they will be found within what has been 

 termed the ano-genital ring, as shown in fig. 7, although they seem 



