HIRUDO. 45 
This creature is very rare. It dwells in some pools opposite Craig- 
crook Castle, three miles west of Edinburgh.* 
Pate V. 
Fig. 20. Hirudo vitrina, back. 
22. Belly, with young adhering. 
21. Head irregulary contracted, enlarged. 
23. Young leech bred from the parent, enlarged. 
§ 11. Hirupo rrava—The Yellow Leech.—Plate V. figs. 1-19. 
This is one of the few leeches which we are enabled to distinguish 
by the form of the head. 
These animals, which are incessantly variable in shape, seldom afford 
such permanent features as contribute to their distribution im natural 
order. Hence we are ready to combine more than one to obtain a suffi- 
cient aggregate of characteristics. Nor do those features depend on the 
external shape of the animal exclusively, for they may beneficially com- 
prehend casual occurrences belonging to the animal. 
The number of the eyes in the individual species of this genus are 
two, as in the d7n-oculata and the present subject ; six in the complanata, 
eight in the octo-oculata, eight in the tessellata and vitrina, ten in the 
medicinalis and sanguisuga. Ihave found no further varieties. But in 
* A single specimen of this species was found by Mr Brightwell in the river at Costessey, 
in the county of Norfolk; which, with a query, he conjectures to be the tessellata. He ob- 
serves that his specimen was nearly cylindrical, about an inch long, colour green, “ with two 
indistinct whitish longitudinal series of spots above, aud two spots underneath ; the whole 
body magnified, appears studded with small dark irregular spots.” He kept this specimen 
about two months. He now found that the young, which were attached to the parent, 
amounted to 143. The eyes of the parent could be scarcely discovered with a lens, those 
of the young were conspicuous. 
It rather appears that this is not the gelatinous leech, though presenting some remote 
analogies in the longitudinal series of spots above—Ann. and Mag. of Nat. Hist., v. ix. 
p- 13. 
