V TAENIA 175 



is now seen to be a typical scolex, with suckers and hooks, which had 

 been inverted into the interior of the cysticercus. 



If a live bladder-worm is swallowed by a dog the scolex becomes 

 everted within its alimentary canal and attaches itself to the lining by 

 means of its hooks and suckers. The vesicle is digested off and the 

 scolex proceeds to grow in length and bud off the chain of proglottides 

 so that it assumes the characters of the typical tape- worm. 



Taenia caninum, another common tape-worm of the dog and also 

 of the cat, is often separated from Taenia as a distinct genus Dipylidium 

 owing to conspicuous differences. Each proglottis has not the typical 

 rectangular form but rather approaches the elliptical — the lateral bound- 

 aries bulging outwards. Further, each proglottis contains a double 

 set of reproductive organs, each with its own openings situated in a little 

 notch which is conspicuous in the middle of each lateral edge. In this 

 case the cysticercus is of very minute size and is often termed a cysti- 

 cercoid. The minute size is correlated with the fact that this phase of 

 the life-history is passed in the body of a dog-louse {Trichodectes) or 

 flea (Pulex). Its occasional occurrence in the human flea is perhaps 

 responsible for the fact that this tape-worm occurs occasionally, though 

 rarely, in the human being. 



Taenia coenurus is a tape-worm which occurs not uncommonly in 

 Sheep-dogs. The bladder-worm stage is remarkable for its great size 

 (up to 2 inches, or even more, in diameter) and for the fact that it 

 produces from its lining not a single scolex but very many scolices 

 which are visible as distinct little white grains through the translucent 

 wall. This bladder-worm occurs in the sheep and a favourite situation for 

 it is the brain where it produces the disease known as sturdy or staggers. 



Among the Cestodes commonly occurring in Man there are four species 

 with which the student should make himself familiar. 



Of these the commonest in Britain and America and other beef- 

 eating countries is T. saginata (Fig. 80, B), a tape-worm which quite 

 usually reaches a length of thirty feet and sometimes much more. 

 A peculiarity of this species is that the scolex is without hooks, while 

 on the other hand the suckers are unusually large and powerful. The 

 shed proglottides — which are what the medical man is most likely to 

 come across — are readily differentiated from those of the next species 

 by the number (20-35 on each side) and slenderness of the branches of 

 the uterus. 



