132 INTERNAL ANATOMY OF INSECTS. 
form tube* ; but there is commonly to be distinguished in 
those that open into the mouth, a reservoir, varying in 
shape in different species, and terminating in a capillary 
tube, or tubes, at one or both extremities b . In Bugs, 
two pair of these vessels are often present, one of which 
opens into the stomach (Reduvius), or gullet (Pentatoma), 
but the other into the instruments of suction c . In the 
Diptera they open into the stomach when the insect feeds 
only upon the nectar of flowers (Syrphus), and into the 
proboscis when it feeds upon both animal and vegetable 
juices (Tabanus, Musca). The function of the fluid se- 
creted by these organs is to moisten or dilute the food 
before it is received by the instruments of suction and 
passed to the stomach d . When a common house-fly ap- 
plies its proboscis to a piece of sugar, it is easy to see 
that it moistens and dissolves it by some fluid. 
iii. Varnish-secretor (Collet erium). In butterflies, 
moths, and several other insects, one or more vessels 
called blind vessels open into the oviduct, concerning 
the use of which, physiologists are not agreed. In the 
cabbage butterfly there is a pair of ovate ones, or rather 
a bilobed one, each lobe of which externally terminates 
in long perplexed convolutions, not easily traced, filled 
with a vellow fluid, which Reaumur and Herold think 
is used for varnishing or gumming the eggs, so that they 
may adhere to the leaves on which they are deposited : 
it may probably serve likewise for other uses*. Another 
vessel is also to be found in the above butterfly, which en- 
a Ramdohr Anat. t. xx.f. 6. D. 
" Ibid. t. xxW.f. 1. K, L.f. 2. I, K, L. 
e Ibid.f. 3, 4, 5. - 1 Ibid. 57—. e Reaum. ii. 81. He- 
rold Expt. of Plates, x. Malpigh. De Bombyc. 37. Plate XXX. 
Fig. 12. c. 
