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-worrn, 
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 Bothriocepltalus must be mentioned. The common¬ 
est species (B. lotus ) 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 Tccnia 
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 
water-fowl, 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 TAPE-WORM (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 
