28 



ENTOZOA. 



the body clothed with little spines ; its general aspect being- 

 altogether very different from that presented by the highest of the 

 phases of development here illustrated. 



The above description may be regarded as offering a fair illus- 

 tration of the mode of development ordinarily taking place in the 

 Trematode parasites, at least, in that (digenetic) division in which 

 we find a double mode of propagation. It does not convey, how- 

 ever, an accurate conception of the various changes which, under 

 certain peculiar conditions, the larvae appear to be capable of 



Fig. l».— The juung or sexudlly immature Disiovia mildure — Van Beneden. 



undergoing ; for it would seem, from Pagenstecher's researches, 

 that their multiphcation and degree of organization are liable to 

 vary considerably, according to the altering conditions of season 

 and weather. On these and many other points connected with the 

 history of the development of the trcmatoda. Dr. Pagenstecher's 

 statements are so extremely interesting that I do not hesitate to 



