MICROSCOPIC OBJECTS. 57 



Fig. 113. Transverse Section of an Echinus-spine 

 (Echinothrix petersii) , x 40. 



The genus Echinus, from which the class Echinodermata 

 derives its name, has many structural beauties, both super- 

 ficial and otherwise. The spines in nearly all the species 

 furnish most beautiful objects when cut in a transverse man- 

 ner with a fine saw, then ground exceedingly thin with a file, 

 and finished on a stone. If they are wanted for the polari- 

 scope, the grinding may be coarser, and they may then be 

 mounted in balsam. The pedicellarise, sections of the shell, 

 &c. also make fine objects. 



The internal structures of these animals are not less inter- 

 esting. 



Fig. 114. ENTOZOON. Head of a Parasite from the Rabbit 

 (Cysticercus pisiformis) , x 30. 



The parasite from which the drawing has been made 

 chiefly inhabits the alimentary canal but is sometimes met 

 with in other parts, as in the liver, where it has been found 

 in the cyst state. Another of the species (Cysticercus tenui- 

 collis] is occasionally met with in the human body. The 

 parasite is something of the shape of a bird's egg, with a 

 neck which may be elongated at pleasure ; the four projec- 

 tions in the drawing are the sucking- disks. This species 

 may be taken as an example of the internal parasites called 

 Entozoa. 



Most of the species show best when mounted in balsam 

 after due preparation. 



