136 INTERNAL ANATOMY OF INSECTS. 
emit scents from their anus, and from various other parts 
of the body, of which having before given you a very 
full account 8 , I shall proceed to the consideration of the 
secretions themselves : but first I must observe, that in 
many cases, as in some of the cottony and powdery Aphi- 
des, Chermes, &c, the substance secreted appears to be 
a transpiration through the pores of the body, a kind of 
excretion from the superabundance of its fluid contents b . 
In many, however, this secretion transpires through ap- 
propriate orifices : thus in Chermes Abietis, which pro- 
duces those curious galls resembling the cone of a fir c , 
the flocoons of seeming cotton that cover it proceed from 
little oval concavities on its back, four of which are ar- 
ranged in a transverse line on each dorsal segment of 
the abdomen : these concavities have minute tubercles 
probably terminating in a pore d . In Aphis Fagi the 
cottony flocoons are almost an inch long e . 
The secretions of insects may be considered under the 
following heads — Silk ; Saliva : Varnish or Gum ; Jelly ; 
Oils ; Milk : Honey : Wax ,- Poisons and Acids ; Odorous 
Jluids and Vapours ; and Luminous matter. 
i. Silk. This valuable product of insects, while in the 
silk-secretor, assumes in the Lepidoptera the appearance 
of a viscid gum, but the moment it is exposed to the air 
it hardens into a silken thread. It is remarkable for the 
following qualities : — it dries the instant it comes in con- 
tact with the air ; it is then insoluble not only in water 
a Vol. II. p. 241—. III. p. 147—. b De Geer iii. 41. 
c Vol. I. p. 451, where by mistake it is represented as the work 
of Aphis Abietis. " De Geer iii. 111. 
* Reaum. iii. /. xxvi./. 4 — 6. 
