442 



THE MICROSCOPE. 



in the Stickleback, becomes changed in the intestines of 

 water birds, which devour these fish; and thus, by careful 

 and repeated observations with the microscope, the con- 

 nexion existing between the Cystic and Cestoid Entozoa 

 have been most satisfactorily established. 



Distomido3 possess two suckers, the anterior of which 

 contains the mouth. One of this genus, and a well-known 



Fig. 215 A. Guinea-worms, taken from Hie leg of a 



1, The form of the worm when first taken from one of the sacs seen at fig. 2. 

 3, A young worm rolled up. 4, Young worm extended. 



example, the Fluke (Distoma hepaticum), infests the livers 

 of sheep. The Polystomidce are characterised by the pre- 

 sence of several suckers at the extremity of the body, but 

 the anterior extremity is either entirely destitute of those 

 organs, or only possesses a small one, in which the mouth 

 is situated. This family includes the singular Diplozoon 

 paradoxum, an animal which appears to be compounded, 

 like the Siamese twins, of two perfect individuals, both 

 having precisely the same organs. 



The common Ascaris, or " Round- worm '* of the human 

 subject, as well as the little " Thread-worm," often so 



