120 



STAEFISH GALLERY. 



Fig. 8. 



events which we find in Tmnia solium, a common Tapeworm of man 

 in Northern Europe (9-15). This worm is matured in the intestines 



of man ; its final joints consist merely of 

 fertilized ova which have already passed 

 through the earlier stages of development ; 

 when the joints are detached and dis- 

 charged, their contents escape in the form 

 of embryos contained in a thick chitinous 

 shell. If these are now swallowed by a 

 pig, the shell is digested by the gastric 

 juices of the new host, and a rounded 

 embryo, which is provided with three 

 pairs of hooks, is set free ; by means of 

 these hooks the guest makes its way 

 through the wall of the stomach or 

 intestine, and finally settles down in the 

 muscles of its host. The embryo now 

 loses its hooks, and gradually acquires a 

 bladder-like form, the central cavity of 

 which is filled with fluid. This bladder- 

 worm (Oi/sticercus) has its outer wall 

 pushed inwards at the anterior end, and 

 on this hooks and suckers become de- 

 veloped. We have now a narrow head 

 and neck with an attached bladder, the 

 head being at this time hollow. If during 

 the long time that these bladder-worms 

 remain alive, the pig is killed for food, 

 its flesh is found to be " measly " ; if it 

 is afterwards insufficientlj cooked and 

 eaten, the worms are conveyed into the 

 human stomach. Here the bladder-like 

 termination becomes absorbed, and, the 

 neck beginning to grow, we have the commencement of the form 

 from which we started, and the completion of that "vicious 

 circle " which is so curious a characteristic of many forms of parasitic 

 life. 



In other Tapeworms the cyst may be more complicated than that 

 in the pig, as, for example, the form found in the sheep's brain (25) 

 or the liver of the horse. 



Of the other Cestode parasites mention should specially be made 



^ \ 



Taenia solium : showing the 

 head (h) with its suckers 

 (s') and crown of hooks 

 (s), the unjointed neck 

 (n), and a few of the 

 succeeding joints (j). 



