386 



RADIATA. 



vered or recognised ; and that, being inconceivably 

 small, they are received with food, or in some other 

 way, into the body, and pass with the blood or other 

 fluids through the minutest vessels to their respect- 

 ive destinations, where, stimulated by constant 

 warmth, and highly nutritive food, they grow to 

 a size which in other circumstances they could never 

 have approached. Either of these suppositions, how- 

 ever, seems beset with almost insurmountable diffi- 

 culties. 



These animals vary much in their structure and 

 form, some being comparatively complicated, while 

 others are very simple. Of the former kind is the 

 Fluke, (Distoma Hepaticum,*) well known as in- 

 habiting the liver of the Sheep, but found also in 

 other animals, and even in Man. It resembles in 

 form a little Sole, about an inch in length, furnished 

 with two suckers, each of which was supposed to 

 contain a mouth, but one of them has been since 

 found to be simple. When sheep are pastured in 

 low wet meadows, this animal often multiplies ex- 

 cessively in them, producing dropsy, or rot, and 

 finally death. 



One of the most singular of all known forms is 

 seen in an animal resembling the Fluke in its internal 

 structure, the Twin-worm (Diplozoon^ Paradoxum). 

 It literally possesses two bodies, each precisely resem- 

 bling the other, and united by a band, which passes 



* Awo, duo, two, and o-rc^a, stoma, a mouth ; and fivartKos, 

 belonging to the liver. 



, diidoos, double, and 2av, zoon, an animal. 



