Acasthocephala. ENTOZOA. Cestoidha. 305 
anterior, containing the mouth, the other imperforated, 
and situated on the ventral surface between the middle 
and the first sixth of the length of the body. The 
intestine is divided into two branches. 
Order IV.— ACANTHOCEPHALA {Rooked 
Worms ). 
The worms be’onging to this order, the Hooked 
Worms, as they are called, are slender, more or less 
elongated, of an ovoid-oblong or cylindrical form, and 
provided with a retractile proboscis, armed with hooks 
or spines arranged in rows. They appear to have 
neither mouth nor digestive tube, but take their nourish- 
ment by absorption. The sexes are separate, and the 
females are oviparous. 
This order contains only one genus, Echinorhynchus, 
the species of which are generally of a round or cylin- 
drical form, and in some instances attain a considerable 
length, though in others the body is shortened to a kind 
of sac. The hooked proboscis is extensile, club-shaped, 
or nearly globular, and the spines are sometimes very 
numerous, being arranged in some species in as many 
as sixty transverse rows. They are chiefly found in the 
alimentary canal of vertebrated animals, and attach 
themselves to the coats of the intestines by means of 
the hooked spines on the proboscis. It is principally 
in Amphibia and Fishes that they are found, but occa- 
sionally they occur in Mammalia. 
Order V. — CESTOIDEA {Cestoid Worms). 
This order includes a variety of worms, which accord- 
ing to Eudolphi and his followers, made a separate 
order by themselves, under the name of Cystic worms 
{Cystica), but which are now better understood, and 
proved to be the immature or undeveloped forms of the 
Cestoid worms. 
The order Cestoidea may be briefly characterized 
thus : — Worms with a soft body, generally flattened or 
band-shaped, and formed of numerous joints. They 
possess neither intestine, mouth, nor vent. They have 
ordinarily a head furnished with two or four suckers 
or small pits which are muscular, very contractile, 
and frequently armed besides with booklets disposed 
in a terminal crown, or in pairs in front of each pit, or 
very numerous upon four or two retractile proboscides. 
The genital organs of both sexes are united, either on 
a single joint or on distinct joints {=Cestoidea). Some- 
times from an arrest of development, there are no 
genital organs, and then frequently the body of the 
worms is terminated by an isolated vesicle, either single 
or common to several {=zCystica). 
Genus T.enia, or Tape-worm. — The worms belong- 
ing to this genus are white, very long, and flat. The 
body is composed of a great number of joints or 
segments very variable in shape and size, and very 
contractile. The head is round or tetragonal, and is 
surrounded by four round, muscular, very contractile 
suckers. In the centre of this head there generally 
issues a proboscis of a greater or less length, and com- 
pletely retractile into a muscular receptacle. This 
proboscis is, in some of the species, naked or unarmed, 
VoL. 11. 95 
but in a great proportion it is surrounded with booklets 
forming one or two rows. The first joints of the body 
are generally very short and numerous ; the middle ones 
are generally broader than long, but of variable shape, 
and provided with more or less distinct genital organs ; 
and the last are filled with ripe ova and then often 
become longer than broad. The genital organs, com- 
plete in each joint, have the orifices situated at the two 
opposite sides of each in some, or at one side only in 
others ; and in this case they ai e either always or gene- 
rally on the same side (unilateral) or they are alternately 
on one side or the other. The last joints are capable 
of being detached and living separately, and each joint 
being a perfect animal as far as the generative appara- 
tus is concerned, the propagation of the species is capable 
of being carried on to a very great extent. The Tape- 
worms are found living in the intestinal canal of verte- 
brated animals, more especially Mammalia and Birds. 
Of late years some exceedingly interesting and very 
curious facts with regard to the development of Tape- 
worms have come to light, and the extraordinary trans- 
formations of Cystic worms into Tainice have been the 
means of enabling naturalists to do away with the 
former as a distinct order altogether. Siebold appears 
to have been the first who advanced the statement, that 
certain Cystic worms were nothing but stray Tape- 
worms which had become vesicular. The Cystic worms 
are generall}' small creatures contained in a cyst, having 
the head furnished with a crown of booklets, and the 
body terminated by a bottle-shaped vesicle filled with 
liquid. They are always destitute of genital organs. 
By a series of experiments made, Siebold ascertained 
that if the Cystic worms which inhabited the body of 
a mouse or rabbit, for instance, were swallowed by a 
dog, these Cystic entozoa of the rodent become in a 
short time, in the intestines of the carnivorous animal, 
a perfect and fully-developed 'Tania. A species of 
Cystic worm (the Cysticercus fascicularis) infests the 
liver of rats and mice. Having previously ascertained 
that certain specimens of these worms were contained 
in the liver of a mouse, the animal was given to a cat. 
Several animals were thus fed, and by killing them at 
certain intervals one after the other, the transformation 
was seen to take place. The liver of the mouse was 
digested in the stomach of the cat, but the Cysticercus 
was left unharmed. It soon loses its terminal or 
caudal vesicle ; and finding in the chyme of the 
stomach and small intestines of the cat a suitable 
place for further development, it speedily assumes 
the articulated form of a Tape-worm. When fully 
developed, the species was ascertained to be the 
common Tape-worm of the cat, the Tania crassicollis. 
Encouraged by the success of this experiment, Siebold 
next tried it with a species which is found living in 
cysts in the coats of the intestines of the rabbit, the 
Cysticercus pisiformis. Several dogs were fed with 
animals infected with these cystic worms, and upon 
killing these dogs at intervals of from two hours to 
eight weeks after being fed, he found these little para- 
sites of the rabbit gradually assuming the form of the 
common Tape-worm of the dog, Tania serrata. First 
he found the cysts disappear, then the terminal vesicle 
becomes absorbed, the worm then quickly begins to 
