AQUATIC WORMS 81 



bore a striking resemblance to the Hydrozoa, yet their general 

 characteristics labelled them definitely as worms. 



The Polyzoa are chiefly marine, but several freshwater 

 species are to be found, in large numbers, more especially 

 towards the end of summer. Every species of the Polyzoa has 

 its views as to the best position for its home. Some species 

 live on the under side of leaves, others choose stones and 

 sticks, whilst a few prefer the submerged roots of willows. 

 Although differing in the choice of situations, in one point 

 they all agree, except Cristatella, for they all dislike sunshine, 

 and prefer shady conditions. Cristatella probably thinks itself 

 more up to date, believing, as it does, in the value of the sun. 

 So, except for Cristatella, we may search for these interesting 

 little animals beneath stones, under the banks, and amongst 

 well-hidden roots in fact, in every conceivable shady place. 

 If luck favours the searcher, a peculiar little colony of Polyzoa, 

 resembling a small mass of jelly, will be found hidden among 

 the dead sticks and leaves. The search is frequently succesful, 

 for although the colonists love shade, yet they have no wish to 

 live at any great depth beneath the surface. 



If we place the captives under a low-power lens, such as the 

 1 inch, and use a 1 or eyepiece, we can not only make out the 

 entire structure, but also see well into the creature. In 

 appearance each little animal resembles a bent tube swollen at 

 one place to form a stomach, whilst the end broadens into a 

 table-like structure, known as the lophophore, on which ten- 

 tacles are borne. The tentacles are fringed with cilia (hairs) on 

 both sides, and each one is able to move independently of the 

 others. The shape of the lophophore, and the number of the 

 tentacles present, is characteristic of the species. Each little 

 animal consists, as we have seen, of a bent tube, one end broad- 

 ened and adorned with tentacles. It is enclosed in a bag-like 

 structure containing a liquid. The contraction of the outside 

 bag forces the liquid into the tentacles, with the result that 

 the creature must necessarily protrude. A muscle fastened to 

 the base of the sack, and to the top, helps somewhat in the 

 movements, more so in those of contraction. The outside case 

 is usually gelatinous and colourless, and so the Polype can be 

 clearly seen within. 



It is most remarkable how rapidly the number of Polyzoa 

 increases. A single specimen in the aquarium at the beginning 

 of the week will probably mean a multitude of colonies before 

 the end of the same week. And this can be easily understood 

 when one inquires into the various means these animals have 

 of reproducing their kind. Firstly there is the sexual method. 



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