VERMES. 63 



few years have revealed the existence of another group of specially 

 modified Holothurians — the Elasipoda ; these are remarkable for 

 their well-marked bilateral symmetry and the distinctness between 

 the dorsal and ventral portions of the body ; the prominent processes 

 on the dorsal surface are not contractile. 



An exhibition of some interest is to be found in a Table-case 

 against the wall, in which there are various specimens of the edible 

 Holothurians — trepang or heche-de-mer ; these were all bought in 

 the market at Canton, and may be taken to be typical of the kinds 

 offered for sale in various eastern countries. 



VERMES. (Worms.) 



Under the head of Vermes (Worms) zoologists are in the habit, 

 at present, of placing 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 any 

 common characters by the possession of which the members of 

 this group can at once be distinguished from other animals. 

 We must therefore take separately the divisions, examples of which 

 are here represented, either by drawings, models, or specimens 

 preserved in spirit. 



Platyhelminthes, or Flat- Worms. — These form the lowest and 

 simplest division of the group. 



The parasitic Platyhelminthes — the Tapeworms (Cestoda) and 

 the Flukes (Trematoda) — occupy Case I. ; the life-history of the 

 common Tapeworm (Taenia solium) is shown by the aid of models 

 and figures. A model of the anterior end of the common Tape- 

 worm shows the four suckers and the crown of hooks ; the un- 

 jointed neck is followed by the joints (proglottids), which increase 

 in size the further they are from the neck. Several entire speci- 

 mens of Taenia 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 Tape- 

 worm is dependent on a migration or a change of the hosts which 

 it inhabits in the various stages of its life ; and although the dif- 

 ferent 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 events which we find in Tenia 



