TAPE-WORMS AS PARASITES 203 
all directions. Those which lie near the surface of the head, and 
penetrate into the tentacles, assume a worm-like form, and are 
brightly coloured with rings of white and green, while the end of 
each of them is marked with a red spot. These tints are easily 
seen through the stretched and translucent skin of the snail. The 
resemblance of these structures to worms is increased by the fact 
that they expand and contract in a rhythmic 
way, and they were at one time actually sup- 
posed to be a kind of para- 
sitic worm, and received a 
special name (Leucochlort- 
dium paradoxum).  At- 
tracted by the colours and 
movement, small birds nip 
off the tentacles of the 
snail, the bright-hued tubes 
of which contain numerous 
tiny flukes that have de- 
veloped within them. The 
fate of these now trembles: sig: gascpicemam wicrostoneime. 4, hk Cand Spall (Sax 
in the: Valance, Vor af they (et ae ay ane 
are swallowed by the adult cae A sporocyst, enlarged, and showing two worm-like 
bird itself they are simply 
digested, but if, on the other hand, they are fed to its nestlings, 
they are able to develop into adult flukes. 
A 
TAPE-WORMS (CEstopa) AS PARASITES 
Creatures resembling Planarian Worms (see vol. i, p. 445) 
were probably ancestral to Flukes, and they, in their turn, stand 
in a similar relation to the degenerate internal parasites known 
as Tape-Worms. In these the peculiar mode of life has had a still 
more far-reaching influence, for there are no digestive organs, and 
the nutriment consists either of the fluids or the already digested 
food of the animals which play the part of hosts. In either case 
it is absorbed by the general surface of the parasite. 
The simplest kind of Tape-Worm known (Archigetes Szeboldz, 
fig. 1152) is a minute creature, less than one-eighth of an inch 
long, which lives within the body of the small Red River-Worm 
(Zubcfex), and there attains the egg-producing stage, which else- 
