90 



INTRODUCTION TO ZOOLOGY 



CHAP. 



water with an undulating motion of the flattened body, or 

 move along the pond-bottom with a " looping " action, cling- 

 ing to the ground with the suckers, of which there is one at 

 each end of the body. 



The Horse Leech (Aulostomum (Haemopsis) gulo) is common 

 in most ponds, the body is 3 or 4 inches long and may be J an 

 inch broad, being wider at the base than at the head end. It is 

 a greenish-black colour on the back and lighter underneath. 



FIG. 46. Horse Leeches in Water. 



The Medicinal Leech (Hirudo medicinalis) is also of a green- 

 ish colour, but has three yellow bands running along each side 

 of its upper surface. This species does not now occur in our 

 ponds, and we only know those that are imported from the 

 Continent. 



The body in leeches is segmented ; the rings, 



Stature nowever > are sometimes very indistinct, each 



segment being subdivided by additional rings. 



At the hind end there is a large circular sucker which is 



used merely for adhesion, and there is also another sucker 



surrounding the mouth. Inside the mouth are three saw-like 



