CESTOID WORMS. 5 IIit 

Hippocrates, Pliny, and Aristotle were familiar with and have des- 
cribed one of those infesting our own species. 
In the adult condition tape-worms are restricted to vertebrates, 
but in the larval or cysticercal stage they infest, a very large pro- 
portion of the animal kingdom, being found in insects and extend- 
ing up to man; in both conditions (larval and adult) they are 
parasitic, mature worm being always located in the bowels of mine 
host, whilst the cysticercus may be found in almost every organ 
and structure of the body. 
It is usual to speak of this living ribbon as a tape-worm, and 
most people are under the impression that it is a single individual ; 
this is erroneous, and examination proves that it is made up of a 
great number of segments, each of which is a distinct animal ; 
they are attached to each other, end to end in single file, the 
whole forming a colony. For mutual advantage, the individual at 
the attached extremity is so modified as to afford means of anchor- 
age for the community ; it is termed the head, of. which there are 
two kinds,—the wxarmed, which has four muscular sucking discs at 
its free extremity, and the armed, which, in addition to the suckers 
has one or more circlets of hooks: both arrangements are merely 
for the purpose of holding fast on to the mucous membrane of the 
bowel. The suckers are in no way adapted for, nor used as 
receptacles for food, and I desire to impress the fact that the tape- 
worm possesses neither mouth, bowel, nor any other digestive 
apparatus whatever ; there is no need for it, because the colony is 
constantly bathed with chyme within the bowel, which as you 
know is that pultaceous material formed from the food eaten by 
the host, and elaborated for the nutrition of his tissues. The tape- 
worm lives then by simply aborbing through its skin the fluid food 
with which it is surrounded ; indeed the tape-wotm is almost 
wholly constructed for the purposes of reproduction, and in this 
particular direction we shall be satisfied, I think, that the organism 
is fairly complete and effective. 
In glancing at the anatomy of these creatures we must notice 
that externally there is a more or less fibrous skin, beneath which 
is a little muscular tissue, after which we find a loose reticulate 
issue or parenchyma, which makes up the interior of the worm 
and envelopes the generative organs. There is also the so-called 
“Water vascular System.” It consists of a single or double tube 
of minute calibre, which runs along the entire length of the colony 
from end to end on each side, with a transverse canal in each seg- 
_ Ment communicating with the longitudinal ones. The use of this 
system 1s rather obscure, but is generally referred to as being partly 
excretory and partly that of conveying a nutrient fluid all over the 
colony, and it is worthy of notice here that this tubular arrange- 
ment 1s the only one that is the common property of the community; 
