574 



THE MICROSCOPE. 



Fig. 257.— Mouth of Leech. 



within the margin of this hole three beautiful little semi- 

 circular saws are situated, arranged so that their edges 



meet in the centre. It is by means 

 of these saws that the leech makes 

 the incisions whence blood is to be 

 procured, an operation which is per- 

 formed in the following manner : 

 No sooner is the sucker firmly fixed 

 to the skin, than the mouth becomes 

 slightly everted, and the edges of 

 the saws are thus made to press 

 upon the tense skin ; a sawing 

 movement being at the same time 

 given to each, whereby it is made 

 gradually to pierce the surface, and 

 cut its way to the small blood vessels beneath. Nothing 

 could be more admirably adapted to secure the end in view 

 than the shape of the wound thus inflicted, the lips of which 

 must necessarily be drawn asunder by the very contrac- 

 tility of the skin itself; and that thn enormous sacculated 

 stomach, which fills nearlv the whole bodv of the leech, 

 was designed to contain its greedily devoured meal, there 

 can be no reasonable question. The leech, in its native 

 element, could hardly hope for a supply of hot blood 

 as food ; and, on the other hand, its habits are most 

 abstemious, and it may be kept alive and' healthy for 

 years, with no other apparent nourishment than what is 

 derived from pure water frequently changed ; even when 

 at large, minute aquatic insects and their larvae form its 

 usual diet." 



In Clepdnidce, the body is of a leech-like form, but very 

 much narrowed in front, and the mouth is furnished with 

 a protrusile proboscis. These animals live in fresh water, 

 where they may often be seen creeping upon aquatic 

 plants. They prey upon water-snails. 



Tubicola. — The worms belonging to this series of 

 branchiferous Annelida are all marine, and distinguished 

 by their invariable habit of forming a tube or case, 

 within which the soft parts of the animal can be en- 

 tirety retracted. This tube is usually attached to stones 

 or other submarine bodies. It is often composed of various 



