76 TURBELLARIA. 



The Guinea-worm {Filaria* Medinensis) is a most troublesome 

 animal in hot climates, where it takes up its residence under the 

 sMn of our legs and feet, and sometimes causes very serious annoy- 

 ance. It is more especially met with on the Guinea coast of Africa, 

 and thence derives its name. This plague of the human race, 

 although not thicker than a knitting needle, sometimes measures 

 upwards of a yard in length : how it gets into its selected abode 

 it is not easy to conjecture; but when once located it seems to 

 make itself quite at home, causing painful tumours : on arriving at 

 maturity it comes to the surface, when it is carefully extracted by the 

 Arab or negro doctors. 



We have in this country a worm of very similar 

 structure, called 



The Hair-worm (Gordius)^, common in summer time in ponds 

 and ditches, so closely resembling in its appearance a hair from a 

 horse's tail, that in former times it was the popular belief that they 

 were really living horse-hairs; their history is somewhat curious. 

 They pass the early part of their life in the interior of some insect, 

 generally a water-beetle, where they grow to the length of ten or 

 eleven inches. 'When full grown, they escape from the body of the 

 poor insect in which they have been nourished, and seek some piece 

 of water, or moist situation, where they deposit their eggs in long 

 chains. 



TURBELLAEIA.j: 



Another large group of worms, although closely 

 allied to the Entozoa, are not parasitic. Their body 

 is flat, soft, and often very contractile, but their chief 

 distinguishing character is that they are entirely 

 covered with cilia, by the movements of which they 

 glide over any smooth surface. They are divisible 

 into two families, the Planar ise and the Nemertes 

 both of which merit description. 



The Planarias (Planaria)^ are to be found abundantly 

 in almost every pond, where they have very mnch the 

 appearance of little sliigs. These animals are of a gela- 

 tinous consistence, and enjoy such a power of self-con- 

 traction, that they can reduce theh whole substance to the 

 form of a speck of jelly, in which condition they occasion- 

 ally force themselves rather disagreeably upon the notice 

 of incautious water-cress eaters. The Planarise inhabit 



* Filum, a thread. 



j Gordius, a man icho tied a very hard knot. 



% Turbella, a commotion, because the action of their cilia makes a 

 stir in the surrounding water. 

 § Planus, ^af. 



