36 HIEUDO. 



PLATE IV. 



FIG. 1. Hirudo complanata ; the Flattened Leech ; adult, back. 



2. Another specimen. 



3. Head of fig. 1, enlarged, shewing the eyes. 



4. Head of fig. 2, enlarged, shewing the eyes. 



5. Margin of fig. 1, enlarged. 



6. Margin of fig. 2, enlarged. 



7. Interanea as displayed after feeding. 



8. Young specimen already propagating ; back. 



9. Belly of the same, with ova. 



10. Belly of an adult, with incipient ova. 



11. Belly of an adult, with numerous ova. 



12. Belly of another specimen, with numerous ova. 



13. Capsule or matrix with ova, enlarged. 



14. Group of young from the capsule. 



15. Young seventeen days old, from the capsule ; back, enlarged. 



1 6. Belly of the same ; the sucker yet inactive. 



8. HIRTJDO STAGNALIS The Pond Leech. Plate IV. fig. 17. 



This is an animal widely diffused throughout Scotland, though, per- 

 haps, not in equal profusion as the preceding. It is smaller, not so broad 

 in proportion, nor alike of varied colours. The largest specimens scarcely 

 exceed an inch in length ; they are of more taper form, and more uniformly 

 grey ; and they dwell in lakes, ponds, or ditches, and in places with but 

 little water, lurking under stones, and especially beneath the bark of 

 decaying trees and branches, where its abode is permanent. Two dis- 

 tinct large black eyes may be observed in the front of this leech, from 

 which the name ordinarily assigned to it is derived. The margin of the 

 body is of peculiar formation, being a series of convexities, forming that 

 kind of border called inverted in the technical language of heraldry. It 

 appears to me that in some perplexed cases regarding identity of species, 

 and perhaps of genera, their solution might be aided by resorting to the 

 margin of the subject. 



On the whole, the pond leech is more slender, and testifies more 

 activity, than the flat leech ; also its adhesion by the sucker is slighter in 



