58 
numbers in certain organs may cause the death of 
the animal which they infest. 
Of the two tapeworms which infest man, Zenza 
solium (fig. w) has, in addition to four suckers, a 
circle of hooks in the middle of the head, which is 
wanting in the second species, 7. sag7zuata (fig. x). 
The latter may grow to the length of four yards, 
and is larger, stronger and more active than 7. solzum, 
which only attains the length of 6 or 8 feet; and 
its sexual organs are more ramified. The Cystecercus 
of 7. solium (fig. y) lives in the pig, and that of 
7. saginata in the ox. But a far more dangerous 
animal is a small tapeworm which lives in the dog. 
If by any chance one of the eggs should enter the 
body of a man, the embryo wanders into various 
organs, usually the liver, where it grows to a Cystz- 
cercus which is sometimes as large as a childs’ head, 
and frequently causes death. - The disease known as 
the Staggers in sheep is caused by Cenurus cerebralis, 
fig. z) which infests the brain; and the corresponding 
tapeworm lives in the dog. 
Fig. zz. Bothriocephalus latus differs from the 
species of Zwnza by its flattened head, with two 
suckers, and by the sexual organs opening on the 
surface of the joints. It is generally found in regions 
where water and fish are abundant; for its embryo 
form is found in \he pike and probably in other fish. 
The sexual animal grows to the length of 24 feet in 
the human intestines, where it may remain for 
20 years; but it is more easily got rid of than the 

species of Zenza. 
Subkingdom Echinodermata. 
(Plate 
The animals of this Subkingdom are principally 
marine, and are usually characterised by the posses- 
sion of spines; and the integument which covers 
the internal contains calcareous 
organs particles 
which are frequently large and numerous enough to 
form a strong external skeleton. The internal struc- 
ture is likewise remarkable, for the separate organs 
are arranged in fives. In addition to the 
digestive, and circulatory systems they possess a 
peculiar structure called the ambulacral system, which 
It 
consists of a ring of water-holding canals round the 
nervous, 
communicates with the surrounding sea-water. 
I. Echinoidea. 
a) Regularia. 
b) Clypeastridea. 
c) Spatangidea. 
II. Asteroidoa. 
a) Astertide. 
b) Ophinride. 
Order I. 
In the Sea-Urchins, the body is enclosed in a 
firm immovable calcareous external skeleton, called 
the Shell. The openings for the sucker-feet are called 
ambulacree and are arranged in rows, and are limited 
to certain plates of the skeleton. All the plates are 
furnished with round regularly-arranged elevations, 
on which are placed movable spines, beyond which, 
however, the sucker-feet always extend. The Sea- 
urchins are round or heart-shaped. They possess a 
curious calcareous masticatory apparatus. 
Fig Echinus sphera, the Common Sea- 
Urchin, belongs to the family Regudarza. The mouth 
and vent are placed opposite to each other, and the 
ambulacre run from one pole to the other. The 
spines are rather short, slender, and of a_ bluish 
colour. This species is eaten on the shores of the 
Mediterranean. 
a els 
oa 
XXIX.) 
mouth, and offshoots penetrate through the pores 
and openings of the skin and the hard outer integu- 
ment, and appear in the form of sucker-feet, which 
effect the progession of the whole animal by  suc- 
cessive adhesion. 
In most species, the sexes are separate, and 
eggs are laid; a few are viviparous. They all creep 
on the ground or over sea-weed, and only swim 
freely in their earliest stages. They are known, 
according to their forms, as sea-urchins, starfish and 
sea-cucumbers. 

III. Crinoidea. 
Holothuroidea. 
a) Fedata. 
b) Apoda. 
c) Hlasipoda. 
Echinoidea. 
Fig. b. Acrocladia mamillata belongs to the 
same order, but differs in the large size of its varic- 
gated spines; it is a native of the Pacific. 
The Clypeastride are shield-shaped, and so 
much flattened that the shell scarcely looks large 
enough to contain the organs of the body. The 
mouth is not placed opposite to the vent, and the 
ambulacree do not run from one pole to another, 
but form a five-leaved rosette. The spines 
very small. 
are 
Fig. c. Scutella hexapora is remarkable for 
the shell being indented with © incisions. 
The Spatangidea, or Heart-Urchins, have no 
masticatory apparatus. The body is heart-shaped, 
and the mouth and vent are placed near ‘together, 
| often on the lower surface. 

