TURBELLARIANS. 57 



about an inch in length, furnished with two suckers, each of which was at one 

 time supposed to be a mouth whence the origin of their name. When sheep 

 are pastured in low wet meadows, this animal often multiplies in them ex- 

 cessively, producing dropsy or rot, and finally causing the death of the poor 

 creatures so infested. 



The Guinea-"Worm (Filaria* Medinensis} is a most troublesome animal in hot 

 climates, where it takes up its residence under the skin of our legs and feet, and some- 

 times causes very serious annoyance. 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-"Wonn (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 some- 

 what 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. 



TURBELLARIA,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 Planarics and the Nemertes both of which merit 

 description. 



The Planarias (Planaria] are to be found abundantly in almost every 

 pond, where they have very much the appearance of little slugs. These 

 animals are of a gelatinous consistence, and enjoy such a power of self-con- 

 traction, that they can reduce their whole substance to the form of a speck of 

 jelly, in which condition they occasionally force themselves rather disagree- 

 ably upon the notice of incautious water-cress eaters. The Planariae inhabit 

 both salt and fresh water, where they swim about rapidly, by an undulating 

 movement of their body, somewhat after the manner of a leech, and creep 

 with great ease upon aquatic plants. They are generally of small size, but 

 exceedingly voracious. Like the Polypes, they appear capable of almost end- 

 less increase by division. Sir J. Dalyell, speaking of the Black Planaria 

 (P. nigra), says, " It is privileged to multiply its species in proportion to the 

 violence offered. It may almost be called immortal under the edge of the 

 knife. Innumerable sections of the body all become complete and perfect 



* Filum, a thread. f Gordius, a man u'ho tied a very hard knot. 



J Turbella, a commotion^ because the action of their cilia makes a stir ii^the sur- 

 rounding water 



