81 



mouth or from the tail ; for I have had himdreds of these lice sucking 

 away at apple-roots in a glass vase for a month, and have thus been 

 enabled carefully to study the mode in which the cottony matter is 

 produced. So far as regards the winged insect, Dr. Fitch expressly 

 says that "the head and the abdomen on its back are covered with d 

 dense mass of Hocculent down;" (ibid.;) and Dr. Harris, speaking of 

 the larva of the true Woolly Plant-louse, says that the cottony down 

 "seems to issue from all the pores of the skin of the abdomen." (Inj. 

 Ins. p. 243.) 



Dr. A. S. Packard, jimr., of Maine, has' published some very 

 amusing and sprightly banter, in ridicule of my theory, that the co- 

 coon of all Gall-gnats [Cecidomyia) is exuded from the general sur- 

 face of their bodies^ not, as in the case of Caterpillars, etc., spun from 

 the mouth, which this author maintains to be the true theory in the 

 case of Gall-gnats. If he had given himself the trouble to read the 

 paragraphs which he undertakes to criticise, he would have seen that, 

 in the case of two distinct species of Gall-gnats, the fact of the cocoon 

 being exuded and not spun has been proved by actual observation by 

 Winnertz and by Osten-Sackeu.* And as to his disbelief in the pos- 

 sibility of any cocoon being exuded from the general surface of the 

 body, if he had ever examined with his own eyes any of these Woolly 

 root-feeding Plant-lice, he would have seen at once that the woolly 

 matter is not secreted from the mouth, nor even from the tail, but 

 from the general surface of the body. ]\Iany other larvae do the same 

 thing. On May 25th I found in a nest of Yellow Ants {Formica 

 aphidicoJa, Walsh,) situated in the decayed stump of a Honey-locust 

 several remarkable woolly larvas, which a month afterwards produced 

 a species of Ladybird (Hyperaspis punctata, Melsh.) These larvae 

 were covered on the back with dense white cottony down, precisely like 

 that of root-lice; on removing some of which lightly with a moist 

 camel's hair pencil, little globules of a yellowish fluid started out 

 from the skin of the larva, evidently from the same pores from which 

 the cottony down had previously exuded. This is the only genus of 

 Ladybirds {Coccinella family) known to me, the larvas of which 

 exude matter of this precise description from their bodies ; but it was 

 long ago discovered that in another genus (Scymnu^) the larvae have 

 their bodies garnished with whitish cottony tufts ; and on examination 

 it will be found that these tufts also are mere secretions from the 

 pores of the body, and not organized appendages like the hairs of a 

 caterpillar or the scales on the wings of a butterfly. The bluish white 



•Compare my Paper Proc. Ihit. Soc. Phil. III. pp. 560j 562 and Dr. Pack- 

 ard's paper ib^d. VI. pp. 214 — 5. 



