116 STAKFISH GALLEKY. 
WORMS. 
By the name "Worms," people commonly indicate a number of 
different forms whose relations with one another are by no means 
so close as those of a Holothurian and a Crinoid, or a Mussel and 
an Octopus. There are not, indeed, any common characters by the 
possession of which the worm-like animals can at once be distin- 
guished from other animals. We take the divisions, examples of 
which are here represented, either by drawings, models, or specimens 
preserved in spirit separately. 
The groups referred to may be enumerated as follows : — 
l Turbellaria. 
h'latyhelmia . . . < 
Trematoda. 
Nemertinea. 
1 Cestoda. 
Nematoidea. 
Chxtopoda. 
Platyhelmia, or Flat-Worms. — These form the lowest and 
simplest division of the group. 
The parasitic Platyhelmia— the Tapeworms (Cestoda) and the 
Flukes (Trematoda) — occupy Case I. ; the life-history of the common 
Tapeworm (Tamia solium) is shown by the aid of models and figures. 
A model of the anterior end of the common Tapeworm shows the 
four suckers and the crown of hooks ; the unjoin ted neck is followed 
by the joints (proglottids), which increase in size the farther they 
are from the neck. Several entire specimens of Tamia follow, 
showing the size of the whole worm and the form of its joints. 
The structure of the body is shown in the models of two joints. 
The growth and development of the Tapeworm is dependent on a 
migration or a change of the hosts which it inhabits in the various 
stages of its life ; and although the different kinds of Tapeworm 
differ from each other somewhat in certain details of their migration 
and development, their life-history exhibits, on the whole, the same 
