Tapeworms. 



61 



FIG. 36. 



be taken as the type of the order. On examination, 



it presents to us a very small roundish head armed 



with twenty-six little hooks arranged in two rows, and 



four round suckers, followed by a long slender neck, 



at first undivided 



but farther down 



exhibiting traces 



of trans verse seg- 



mentation,which, 



as we trace the 



worm from the 



head, become 



more and more 



clearly marked 



until we reach a 



narf rnncMchncr A > Proglottis, or perfect joint of Tapeworm (Ttznia- 



.Ibling So!ium ) x 2 ^ rt> water-vascular tube ; b, vulva ; 



Of distinct Se2f- ^> uterus ; d, spermatic gland ; e, vesicula semi- 



& nalis \f y vas deferens : 

 each Of B, Head of Teenia inedio-canellata x 20. 



which contains a complete egg-producing apparatus. 

 When we remember that these worms may attain 

 the length of 25 feet, and that there are at least 

 twenty perfect joints in a foot, and that each joint 

 can produce many scores if not hundreds of ova, 

 we can form some idea of the amazing fecundity of 

 these parasites. The growth of the individual takes 

 place from the head, so that the oldest segments are 

 those which are most remote from it and the newest 

 are the fine joints close thereto. 



The life history of the tapeworm is curious. The 

 eggs are protected by a very firm horny capsule and 

 thus they can maintain their vitality for long periods 

 of time, and can resist maceration and even short 



