TRANSMIGRATIONS AND METAMORPHOSES. 



241 



The Ascarls acus of the pike lives at first in a common 

 white fish, the Leuciscus alburniis, and passes with this 

 fish, which serves it as a vehicle, into its final host. 



Another common nematode, the Oxyurus vermicularis 

 (Fig. 69), a parasite of man, is a small worm of the size 

 of a fine pin, which often multiplies in the rectum of 

 children, causing intolerable itching. It is by means of 

 their microscopic eggs that they penetrate into the 

 system ; these are hatched in the stomach, and are com- 

 pletely developed at the end 

 of eight or ten days. They 

 pass from the anus in great 

 numbers. 



Fig.es.— Tricliocephalusof man.— 1, female. Fig. 69.— Oxyurus vermicul^ns— 1, male of 



a, cephalic extremity, b, caudal extremity 

 and anus, c, rf, digestive tube and ovary, 

 e, orifice of sexual apparatus. 2, isolated 

 egg. 3, male, a, cephalic extremity, b, 

 anus, c. digestive tube, d, spicula or penis, 

 e, sheath Into which it is withdrawn. 



natural size, 2, female, id., 3, cephalic 

 extremity, magnified. 



The brood of worms from the eggs of the Ascar'is 

 megalocejyJiala of the horse live in freedom, and go 

 through all their phases until their sexual develop- 

 ment separately; there are males and females. The 



