T^NIA SOLIUM 



129 



^■te* 



with longitudinal muscle fibres between them and a transverse 

 layer of muscle below them. Inside this is a mass of parenchyma 

 like that of the fluke, in which are embedded the excretory, genera- 

 tive, and nervous systems. There is no alimentary canal, nutriment 

 being absorbed through the surface of the body. There is a 

 flame-cell system of the same type as that of the fluke, with 

 a larger and a smaller main duct on each side, connected by 

 a transverse vessel on the hinder side of each proglottis. In the 

 last proglottis these vessels open by a median pore. The nervous 

 system consists of a ring in the head, small forward nerves, two 

 lateral nerve cords and branches. 



REPRODUCTION 



The reproductive organs have 

 the same general structure as in 

 the liver fluke : they are shown in 

 Figs. 92 and 93. Each proglottis 

 contains a complete set of them. 

 Since no other worm is usually 

 present, it must be fertihsed 

 either by another proglottis or 

 by itself. From time to time the 

 last proglottis breaks off, singly 

 or with others, and passes out 

 of the anus of the host. It is not 

 able to crawl about, although 

 that of the related beef tape- 

 worm T. saginata can do so, 

 discharging eggs as it goes. The 



eggs, to the number of 850,000 or more, are set free by the rupture 

 of the proglottis wall. If, as may happen in various circumstances, 

 they are now swallowed by a pig, or, as occasionally, by man, their 

 shells are dissolved in the ahmentary canal and a httle spherical 

 six-hooked embryo or oncosphere is set free from each. This 

 bores its way from the intestine of the host into his blood vessels 

 and is carried to the muscles and other organs, where it loses its 

 hooks, increases in size, and becomes a bladder-worm or cysticercus. 

 The wall of this becomes tucked in at one spot, forming a pouch, 

 on the inner wall of which the suckers and hooks of the future 

 head appear. This happens ten weeks after the e^g has been eaten 



Fig. 92.^ — A proglottis of Tcsnia solium 

 with the reproductive organs at the 

 stage of complete development. 



C.S., Cirrus sac ; excr. excretory canals ; g.o., genital 

 opening ; n.c, nerve cord ; ov., ovary ; sh.g., 

 shell gland ; t., testes ; v.d., vas deferens ; ut. 

 uterus ; vag., vagina ; y.g., yolk gland. 



