FLAT -WORMS, 



463 



Tcema echinococcus (enlarged). 



abundance in dogs and cats. Many other tape-worms live in these mammals, one 

 of the commonest infesting the former being T. serrata, distinguished by a double 

 row of hooks on the head. In the bladder- worm stage this species lives in rabbits 

 and hares. The commonest form in cats is T. crassicollis, which has a large head 

 and a short thick neck, its bladder- worm stage being passed in mice. Perhaps, 

 however, the most important tape- worm of the dog is T. ccenurus, interesting on 

 account of the remarkable features it presents in its condition as a bladder-worm, 

 and the serious disease, known as the staggers, which its presence in the brain 

 brings upon sheep. Another pest of much the same 

 nature is the bladder -worm known as Echinococcus. 

 The mature worm living in the dog is a small tape- 

 worm, scarcely more than a sixth of an inch in length, 

 and differs from the species hitherto discussed, in that it 

 consists merely of a head, neck, and three distinct 

 segments, of which the third or last becomes ripe and 

 then equals the rest of the worm in length. The head, 

 like that of T. solium, is furnished with suckers and 

 hooks, and the embryo which hatches from the egg is 



armed, like the rest, with six hooks. The bladder- worm stage occurs in both men 

 and pigs, and each bladder becomes the brooding-place of a large number of others. 

 Upon the surface of the bladder several ingrowths are developed, and each of 

 these gives rise to a single head. As many as twelve, fifteen, or twenty may be 



formed. The bladder, however, sometimes becomes more 

 complicated by the formation, either outwardly or inwardly, 

 of secondary head-producing vesicles, so that the original 

 cyst is enveloped by others which have arisen as its 

 buds. To complete the register of the tape-worms, whose 

 life-histories are bound up with our own existence, the 

 genus Bothriocephalus must be mentioned. The common- 

 est species (B. latus) is the largest of human tape- worms, 

 and may attain a length of nearly 10 yards, and be 

 furnished with from three to four thousand segments. It 

 may be at once distinguished from the species of Tcenia 

 by the shape of its head, which is long, flattened, and 

 furnished with a deep cleft or slit on each side. The 

 intermediate hosts of this worm are fresh -water fish. 

 Belonging to the same class as the preceding is the strap- 

 worm (Ligula simplicissimci), which reaches maturity in the intestine of various 

 water-fowl, but is found in the bladder-worrn stage in the body-cavity of whiting, 

 which swallow the eggs expelled from birds. A peculiarity of this worm is, that 

 the segmentation of the body into proglottides does not take place. 



BROAD TAPE-WOKM (Bothrio- 



cephalus). a, Head nat. 

 size ; b, Head enlarged ; 

 c, Segments. 



TREMATODE WORMS, Order Trematoda. 



Some of the less highly organised members of the preceding group, namely, 

 those which are not segmented, are nearly related to the present section of 



