43 THE ENTOMOLOGIST. 



time was — and still is — that the dust surrounding the cocoon, 

 and which is wonderfully light, and set floating in the air by the 

 slightest touch, is the medium by which the poison — for poison 

 undoubtedly it is — is conveyed to the skin. 



I j&nd from an exhaustive and thoughtful paper in ' Psyche ' 

 (vol. iii., nos. 101 & 102), the organ of the Cambridge (Mass. 

 U.S.A.) Entomological Club, which the editor, George Dimmock, 

 Esq., has kindly sent me since my note appeai-ed in the 

 * Entomologist,' that both American and Continental scientists 

 appear to be ahead of us in this branch of Entomology. 



Perhaps I may be excused, considering the paucity of informa- 

 tion which we appear to possess on this subject, for making a 

 few quotations from Mr. Dimmock's paper " On some glands 

 which open externally on insects." Speaking of the larva of 

 Attacus cecropia (and there is a strong presumption that what is 

 true of one hairy larva is true, in a more or less degree, of 

 others), he says: — "The red tubercles are seen, in sections cut 

 with the microtome, to be divided into compartments, the cavities 

 of each spine opening into a compartment at its basal end. The 

 spines themselves are quite rigid and very brittle, so that they 

 break away at a slight touch and leave a hole in the tubercle, out 

 of which an odorous fluid pours, pushed by internal pressure. 

 This fluid is strongly acid to litmus paper. The odour given out 

 by these glands suggests at once their protective functions. . . . 

 Glands similar to those of the larva of Attacus cecrojna, in that 

 they have no outlet until one is produced by external agenc}^ are 

 not rare in the larvae of Bombycidse. The severe poisoning pro- 

 duced by the hairs of certain larvae of Bombycidse, of which the 

 so-called processionary caterpillar of Europe is an example, is 

 caused by the secretion from a minute gland at the base of each 

 hair. The secretion of these glands fills the hollow central 

 portions of the hairs, and when the sharp, often barbed, hairs are 

 broken in the flesh of attacking animals, the broken parts carry 

 with them the poisonous secretion. This secretion is, perhaps, 

 formic acid, or a formate in solution." 



As Mr. South mentions Cnethocampa (Entom. xviii. 5) I give 

 the following : — " Goossens regards the spines of the larvae of 

 Cnethocampa to be poisonous because of a powder produced by 

 the drymg of the secretion given out by the evaginable glands 

 upon the dorsum of these larvae. This view seems unacceptable 



