282 PEESH-WATEE AQTTAKIA. 



some excuse for imagining it to be an animated horsehair. 

 The male Haii* Worm may be distinguished from the female 

 by its forked, or bifid, tail. The head-end of both the sexes 

 is round. These creatures seem to have no m.outh, and 

 appear to obtain what nourishment they require by absorp- 

 tion through the skin. Their power of resisting the ill-effects 

 of drought is so great that they may be taken out of the 

 water and exposed for some hours to the scorching rays of 

 the sun, until they look as if they were quite dead and dried 

 up into almost nothing, and then when returned to the 

 aquarium or pond they will soon regain both the fife they 

 seemed to have lost and their former activity. They swim in 

 a most graceful eel-like manner. Hair Worms are oviparous 

 and deposit their eggs in strings. 



G. aquaticws is an entozoon : that is, it spends some portion 

 of its life within some other animal. When a beetle, for instance, 

 has fallen by accident into water, or has been driven there 

 by instinct, a Hair Worm wiU sometimes be seen emerging 

 from the unfortunate creature, having been for long its unwilling 

 host. These remarkable creatures may occasionally be seen in 

 great nimabei-s swimming about the shallowest parts of rivers 

 and ponds, or entwining themselves among the aquatic weeds 

 growing there. 



The aquarium-keeper, during his hunts for aquatic animals, 

 frequently finds certain little fluke-like creatures, crawling 

 over or clinging to the mud, weeds, or stones of the water. 

 These animals are known as Planarian Worms. They may 

 be found during any season of the year and in nearly every 

 pond, lake, or slow-running stream. They are of various 

 colours. There is, for instance, a white species {Plana/ria 

 lactea), a brovfn (P. brunnea), and a grey (P. torva) ; but the 

 commonest of all is the Black Planarian [Polycelis nigra). 

 These worms have soft and gelatinous bodies, which quickly 

 decompose after death. The Planarise are both interesting 

 and useful in the aquarium. They are interesting principally 

 because they have the power of reproducing lost parts of 

 their bodies, and also because even their number may be 

 increased by cutting them in half ; and they are useful 



