SCOLECIDA. 119 
worm, or Tenia solium. The common tapeworm is found in- 
habiting the intestines of man, one only being generally present 
in the same individual. In shape (fig. 50, 5) it is an extremely 
elongated, flattened, tape-like body, many feet in length, and 
composed of a number of flattened joints (fig. 50, 4) all loosely 
-united to one another. At one extremity the joints become 
much smaller and narrower, till ultimately a point is reached 
where the organism is firmly fixed to the mucous membrane of 
the intestine by means of a minute rounded head (fig. 50, 3). The 
organs by which attachment is effected are, in this species, a 
crown of recurved hooks and four suckers. The head is in 
reality the true animal, and all the long, jointed, tape-like body 
which follows this, is really produced by a process of budding 
from the head. The head contains no reproductive organs, 
and is not furnished with a mouth or digestive organs of any 
kind, its nutrition being entirely effected by imbibition of the 
nutritive fluids elaborated by its host. A nervous system, in 
the form of one or two ganglia, sending filaments backwards, 
is said to be present; but there is some doubt on this point. 
The water-vascular system (fig. 50, 4) consists of two long ves- 
sels which run down each side of the body and communicate 
at each articulation by a transverse vessel, the whole opening in 
the last joint into a contractile vesicle. Each joint is sexually 
perfect, or hermaphrodite, containing both male and female re- 
productive organs (fig 50, 4), which open on the surface by a 
small raised aperture, the ‘‘ generative pore.” Almost the whole 
of each of the mature joints is filled up by a much-branched 
ovary. As the head is the true animal, and the numerous joints 
are only produced by budding, it follows that the entire organ- 
ism is to be regarded as a kind of colony, constituted by a single 
sexless zodid or “ nurse,” and numerous sexual zodids, produced 
by budding from the former. 
The process of development—that is to say, the process by 
which this composite organism, commonly known as the tape- 
worm, is produced—is a very remarkable one, and is briefly as 
follows: Each generative segment or joint, as already said, is 
hermaphrodite, and contains innumerable ova. These eggs, 
however, cannot be developed within the body of the animal in- 
fested by the tapeworm itself, but they are compelled to gain 
access to the body of some different species of animal, if de- 
velopment is to proceed. To secure this end, the mature joints 
