274 THE MICKOSCOPE. 



forms and appearances are to be met with, differences owing to decom- 

 position or to mechanical injury ; and in many cases no trace of them 

 can be found except the booklets or spines, which, like the fossil re- 

 mains of animals in geology, remain as certain indications of their 

 source, and not unfrequently afford the only proof we can obtain of 

 the true nature of the hydatid. 



In almost all the aggregations of Echinococci, besides the perfect 

 specimens, there are to be seen one or more of a different appearance 

 and of various shapes round, clavate, or oval like the others, attached 

 to the common mass by a pedicle : they are composed of granular mat- 



fig-. 118. JEcMnocoeci found in the human liver, magnified 250 diameters. 



ter, denser apparently, and of a deeper colour, than that of which the 

 bodies of the perfect animals are composed, and increasing in density 

 towards the free extremity." 



ANNELIDA. 



The Annelida, in general, present a more complicated organisation 

 than any of the preceding animals ; the division of the body into seg- 

 ments is usually distinctly recognisable, and the segments are almost 

 universally furnished with external appendages, which are sometimes 

 jointed. The majority live in water, or in damp situations ; a very 

 few only are parasitic in their habits. 



