114 Mr. O. H. Latter on the Prothoracie Gland of 
excessively. Hxamination of this deposit revealed 
shreds of the walls of the silk glands scattered through- 
out the sheet. It at unce occurred to me that if this 
effect was produced by the action of hydrochloric acid 
upon the contents of the silk glands, it was possible that 
the formic acid secreted by the prothoracic (‘‘ neck ”’) 
glands, as described by Klemensiewicz (8) and Poulton 
(12, 13) might perhaps in a similar way give rise to the 
peculiar horny and non-fibrous character of the silk of the 
cocoon of this species. ‘This suspicion was rendered the 
more strong by the fact that the sheet taken from the hydro- 
chloric acid when exposed to the air and allowed to dry 
assumed in the course of a few hours an appearance and 
consistency very similar indeed to that of a Vinwla cocoon 
spun without fragments of wood, etc. Unfortunately I 
was unable, in consequence of want of material, to 
proceed further with the subject in 1895, and accordingly 
was obliged to defer the work till the summer of 1896, 
when I procured a large number of larve from Messrs. 
Edmonds of Windsor. My first. step was to determine 
whether formic acid behaved towards the excised silk 
glands in the same manner as hydrochloric acid. <Ac- 
cordingly the silk glands of a fully grown larva were 
dissected out and at once placed in formic acid, and there 
cut up into several pieces. In the course of a few hours 
the whole mass had swollen greatly and had set into a 
tolerably firm and nearly transparent jelly. On exposing 
this jelly to the air so as to permit evaporation, shrink- 
age took place, and eventually there was left a hard 
horny mass very closely resembling a cocoon both in 
texture and appearance. I may here add that I treated 
the silk glands of several other species, notably of JL. 
cossus and of the larva of the Japan Silk-Moth, 4. pernyz, 
witb formic acid in the same way but with totally differ- 
ent results. The glands of Z. cossus remained flaccid, 
but became whiter and more opaque, while those of A. 
pernyt became very tough and much harder. It is thus, 
evident that a special relation exists between the com- 
position of the undischarged silk of D. vinulw and formic 
acid, and it is further probable that the chemical com- 
position of the silk of various species is very far from 
constant. 
I next endeavoured to ascertain whether the larva did 
as a matter of fact employ its formic acid when con- 
