CHAPTER V 



WORMS. ROTIFERS, LEECHES. POLYZOA 



THE Worms comprise a great assemblage of animals of most 

 diverse character and shape, leading the most varied lives, some 

 dwelling in the sea, others in brackish and fresh water, others 

 on land ; while a whole host lead a parasitic existence in the 

 tissues of human beings, in wild and domestic animals, birds, 

 reptiles, and insects. To most people the vast majority are un- 

 familiar, if not absolutely unknown ; nor can they be said to 

 have any common characters by the possession of which they 

 can at once be clearly distinguished from other animals. They 

 are essentially an assemblage of animals of more scientific than 

 popular interest, and have received more attention from the 

 specialist than from the amateur. At the same time they are a 

 very important group, and many of the marine forms are of 

 extreme beauty and interest. 



The lowest and simplest division of the group are the so-called 

 Flat- worms (Platyhelminthes) , which include the free Flat- worms 

 (marine, fresh water, and terrestrial forms), the Flukes, and the 

 Tape-worms. Leptoplana trcmellaris is a common representative 

 of the marine dwellers, often to be found buried in the mud, or 

 under flat stones in the tidal pools, which has gained its name 

 from the tremulous or quivering movements of its thin body as 

 it swims along, the motion of the side expansions of the body 

 somewhat resembling the action of a ray as it swims through the 

 water. The body of Leptoplana is flat, soft, unsegmented, broader 

 at the anterior end, tapering somewhat towards the posterior. 

 It is brownish in colour, and measures from J to I inch in length. 

 Eggs are attached during the spring and early summer to stones 

 and seaweeds, and the young hatch out in two or three weeks, 

 and at first swim about in the surface waters until they are about 

 4 millimetres in length, when they are often very numerous 



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