fcRANSMIGBATIONS AtiD METAMORPHOSES. 



241 



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

 white fish, the Leuciseus albwnus, 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 intolerahle 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. (B.-Triohooephalua of man.-l, female, Fig. 69.-Oxynrus vermioularis.-l, .male of 

 I, oephallo extremity, 6, caudal extremity natural size, 2, female, id, 3, cephalic 

 and anus, c, d, digestive tube and ovary, extremity, magnified. 



e, orifice of sexual apparatus. 2, isolated 

 egg. 3, male, a, cephalio extremity, o, 

 anus, o, digestive tube, d, splcula or peniB, 

 e, sheath into which it is withdrawn. 



The brood of worms from the eggs of the Ascaris 

 megalocejphala of the horse live in freedom, and go 

 through all their phases until their sexual develop- 

 ment separately; there are males and females. The 



