60 Invertebrata. 



feed. The digestive canal in the smaller flatter forms 

 is often tree-like, branched (fig. 35). In others it is a 

 simple pouch with no anal orifice ( Aprocta), but in the 

 larger forms it is elongated with an outlet (proctuchous). 

 The water- vessels appear as two lateral tubes, and the 

 egg-producing organs are complex. The proctuchous 

 Turbellarians on leaving the egg are unlike their 

 parents, often helmet-shaped, with a whiplash-like 

 process at the apex, and this larva develops into a 

 worm-like body by moulting or shedding its surface. 

 The smaller aproctous forms are generally flattened and 

 elliptical ; the proctuchous are worm- like, sometimes 

 very long, and are called Nemertean worms. One of 

 these, Borlasia, found not uncommonly on our own 

 shores, has been taken measuring twelve feet in length. 



The 2nd, 3rd, and 4th classes of worms are mostly 

 parasitic in their habit and are called suctorial, round, 

 and thorn-headed worms respectively. 



CLASS II. Cotylidea. The sucker-bearing worms 

 are so called because they are armed with rounded or 

 irregular cup-like suckers. These worms have generally 

 become, by a process of degradation due to their habit, 

 simple in organisation ; and their body cavities and 

 digestive organs are either abortive or rudimentary. 

 The types of these worms are Tapeworms and Flukes. 



The tapeworms are so called from their great 

 length and flatness. They exist principally in the 

 digestive canals of higher animals, especially in fishes. 

 The human race is occasionally not exempt from 

 harbouring at least three species of these parasites. 

 One of these, the common tapeworm, or Tcenia Solium, 

 is common in Britain and Western Europe, and may 



