343^ 



THE WORM-LIKE ANIMALS 



Tcenia echinococcus. 

 (Enlarged.) 



however, the most important tapeworm of the dog is T. c<znurus, 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 w r ith 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 tapeworms, 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 tapeworms, 



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



furnished with from three to four thousand segments. It 



may be at once distinguished from the species of T&nia 



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 simplicissima} , which reaches maturity in 



the intestine of various waterfowl, but is found in the bladder worm 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 TAPEWORM (Bo- 

 thriocephalus). a. Head 

 natural size ; b. Head 

 enlarged; c. Segments. 



TREMATODE WORMS Order TREMATODA 



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

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

 worms. In this class the body is unsegmented, usually leaf-like in form, smooth 

 skinned, and provided with suctorial discs in the middle or at its hinder end. 

 There is a distinct digestive canal, usually forked, but provided with only one 



