SECT. v. EXTOZOA. i47 



longitudinal and circular fibres, by means of which they 

 can stretch and contract themselves. They are gene- 

 rally pointed at both ends with a mouth at one ex- 

 tremity and an orifice at the other. The Filarise are 

 slender, sometimes of great length, as the Guinea worm, 

 which varies in length from six inches to two, eight, or 

 even twelve feet. In Persia they are believed to be in- 

 troduced into the system by drinking water in which 

 their eggs have been deposited. This worm may grow 

 in the muscles of a man to the size of five or six feet 

 without giving much annoyance, but when its head 

 bores through the skin it produces a painful sore unless 

 extracted. In Persia, where the worm is common, the 

 natives seize it by the head, draw it carefully out, and 

 wind it round a bit of wood, an operation which may 

 require several days to accomplish. It has a numerous 

 viviparous progeny, which come out through the mouth. 

 There are certain very small slender species of Filaria 

 which attack the eyes both of men and horses ; some 

 bury themselves close to the eye, and a very minute kind 

 enters the ball itself. 



The Ascaris lumbricoides, a common intestinal thread- 

 worm of the hog, ox, and the human race, is sometimes of 

 great length. The sexes are distinct, and their fertility 

 enormous. The ovaries are two tubes sometimes several 

 feet long, in each of which the eggs are arranged in 

 whorls round a central stem, like the flowers of a plantago. 

 By counting the number of microscopic eggs in a whorl, 

 and the number of whorls, Dr. Eschricht ascertained 

 that in a full grown female the average number of eggs 

 amounted to sixty-four millions. In this species of 

 worm the embryo is not developed from the egg while 

 within the victim, so that most of the eggs perish. 



Different species of Anguillulse, which are minute 

 eel-like worms slender as a hair, inhabit the alimentary 

 canal of fresh-water snails, frogs, and fishes, but many 



