INTERNAL ANATOMY OF INSECTS. 105 
with in the Coleoptera*. In caterpillars, the tops of these 
vessels perforate the outer skin of the rectum, and pro- 
ceeding in dense convolutions to the anus, become at last 
so fine that their terminations cannot be discovered?. 
In other cases, the extremities of a pair of these vessels 
unite so as to form a double one: this may be seen in 
those of Staphylinus politus*, and probably other rove- 
beetles: and lastly, in others the bile-vessels are free, 
hanging down by the intestinal canal, without being at- 
tached to it or to each other. ‘This structure is con- 
stantly found in the Orthoptera and Hymenoptera Or- 
ders, &c.4. 
With regard to their number, the bile-vessels vary from 
two to upwards of one hundred and fifty, yet so that 
their whole amount is constantly the product of the num- 
ber two,—at least as far as they have been counted: and 
even when those on one side are not alike, a similar va- 
riation takes place in the other, as may be seen in Gal- 
leruca Vitelline, where on each side are two long ones 
and one shorter®; the most usual numbers are, four— 
siz—or many, that is, more than twenty— 
Two bile-vessels are found in the larva of Cetonia aurata'. 
POUL ceccacsscdsversacosseveevee. Most Coleoptera, Diptera, 
and Hemipteras’. 
SUX dies cevcrsecsocotcsocsvesdss Lepidoptera, some Colzo- 
ptera®, &c. 
a Tbid. 45. > Tbid. 45. Prats XXI. Fic. 3. ff. 
© Ramdohr, Jdid. t. ui. f. 6. E. 
4 Ibid. t.i. f. 1.5 9. t. xiv. fi 1—3. © Ibid. 46, t. vi. f. 3. 
£ Tbid. t. vii. f. 2. ® Tbid. t. i. ii. &e. t. xx. f. 1,2. 6. 
t, xxl. f. 1—5. &e. N Thid.t. xvataf. 1. 5. tiv. 7. V. See 
also ¢t. vi. f. 1. 3. 
