26 



STUDIES IN ANIMAL LIFE. 



fully remove a drop of the liquid found inside, 

 which, on being brought under a microscope, we 

 shall most probably find containing some animal- 

 cules, especially those named Monads. These were 

 not swallowed. They live in the cerebro-spinal 

 fluid, as the Opalina lives in the digestive tube. 

 Nay, if we extend our researches, we shall find 

 that various organs have their various parasites. 

 Here, for instance, is a parasitic worm from the 



frog's bladder. Place it 

 under the microscope with 

 a high power, and behold ! 

 It is called Polystomum 

 many-mouthed, or, more 

 properly, many-suckered. 

 You are looking at the un- 

 der side, and will observe 

 six large suckers with their 

 starlike clasps (e), and the 

 horny instrument (/) with 

 which the animal bores its 

 way. At a there is anoth- 

 er sucker, which serves 

 also as a mouth ; at b you 

 perceive the rudiment of a 

 gullet, and at d the repro- 

 ductive organs. But pay attention to the pretty 

 branchings of the digestive tube (c), which ramifies 

 through the body like a blood-vessel. 



This arrangement of the digestive tube is found 



Fig. 3. POLYSTOMUM INTEGEEEI- 

 MTTM, magnified. 



