276 THE MICROSCOPE. 



blood-vessels beneath. Nothing conld 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 

 contractibility of the skin itself; and that the enormous sacculated 

 stomach, which fills nearly the whole body 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 the Clepsinidce, the body is of a leech-like form, but very much 

 narrowed in front, and the mouth is furnished with a protrusible pro- 

 boscis. These animals live in fresh water, where they may often be seen 

 creeping upon aquatic plants. They prey upon the water-snails 

 (Limnece). 



Some species of this family, forming the genus Piscicola, live as 

 parasites upon various fresh-water fishes ; whilst those of the genus 

 BranchiobdeUd) which are quite destitute of eyes, inhabit the branchia3 

 of some Crustacea. The Scolecina, of this order, the well-known earth- 

 worm so common in our gardens, is an example. Naids are inhabi- 

 tants of water. 



The Tubicola. The worms belonging to this series of branchiferous 

 Annelida are all marine, and are distinguished by their invariable habit 

 of forming a tube or case, within which the soft parts of the animal 

 can be entirely retracted. This tube is usually attached to stones or 

 other submarine bodies. It is often composed of various foreign 

 materials, such as sand, small stones, and the debris of shells, lined in- 

 ternally with a smooth coating of hardened mucus ; in others it is of 

 a leathery or horny consistency ; and in some it is composed, like the 

 shells of the Mollusca, of calcareous matter secreted by the animal. 

 These animals frequently live together in societies, winding their tubes 

 into a mass which often attains a considerable size; others are more 

 solitary in their habits. They retain their position in their habitations 

 by means of appendages very similar to those of the free worms, and 

 furnished like these with tufts of bristles and spines ; the latter, in the 

 tubicolar Annelid es, are usually hooked ; so that, by applying them to 

 the walls of its domicile, the animal is enabled to oppose a consider- 

 able resistance to any effort to draw it out of its case. 



In the best known family of the order (Sabellidce), the branchiae 



