HI11UDO. 45 



This creature is very rare. It dwells in some pools opposite Craig- 

 crook Castle, three miles west of Edinburgh.* 



PLATE V. 



FIG. 20. Hirudo mtrina, back. 



22. Belly, with young adhering. 



21. Head irregulary contracted, enlarged. 



23. Young leech bred from the parent, enlarged. 



11. HIRUDO FLAVA 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 in 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 bin-ocnlata and the present subject ; six in the complanata, 

 eight in the octo-oculata, eight in the tessellata and mtrina, ten in the 

 medicinalis and sanyuisuga. I have 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, and 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., \. i.\. 

 p. 13. 



