WORMS. 



235 



growths, or (in Echinococcus, Fig. 138) several new 

 bladders are developed inside the bladder- worm, and 

 ingrowths are usually formed within these, similar 

 to those of the simpler kinds of bladder-worm. 

 These ingrowths resemble tapeworm heads in all 

 respects, possessing suckers, and, it may be, a circlet 

 of hooks, but these are inside, and not outside. 



loenarus 



£ohineoeeeus 



Fig. 138.— The three types of Bladder-worm, diagrammatically represented. 



Later — either in the animal originally inhabited by 

 the bladder-worm, or after it has been transferred in 

 the flesh of this to the gut of some carnivorous 

 animal — the bladder-worm con- 

 tracts, so that it can no longer 

 hold the fluid which is present, 

 and the ingrowth is turned inside 

 out, the suckers thus becoming 

 external. The tapeworm head is 

 formed in this way, but the bladder 

 still remains attached to its hinder 

 end (Fig. 139). If a host in- 

 habited by bladder-worms is not 

 devoured by another animal, the 

 bladder-worms, after reaching their full size, remain 

 for a long time in the same stage of development 



Fig. 139.^Measle of T. so- 

 lium, with head thrust out 

 CX6). 



