358 TNSECTi} IXFESTfNG DOMESTIC ANIMALS. 



and moreover, without nerves, of which there are l)ut mere 

 traces, these organs would he entirely useless, even if they 

 were in the light. That they do possess eye-like spots at a 

 certain stage of their life is true ; but there is nothing to show 

 that these are organs of sight or eyes in. any true sense. What 

 this author considers the heart and circulatory system is prob- 

 ably the water vascular system, found in these and all other 

 animals belonging to this class, which is supposed b}'^ many to 

 represent the respiratory system in the higher grades. He 

 also supposes that the eggs or spores, after being cast off, re- 

 main undeveloped until taken into the stomach Vn' the siieep 

 with its food, which, as will be seen, is an error. 



" The species belonging to this order vary consideraljly in 

 their transformations and habits, some passing through a cycle 

 of six forms, while others present only three or four. ^?ome 

 infest the liver or hepatic ducts of vertebrates; others infest 

 the intestines of birds and batrachians,'the gills of fishes or 

 paunch of ruminants, while others are found imbedded in the 

 vitreous humour and lens of the eyes of certain fresh water 

 fishes, such as the perch. 



" The cycle of changes through which the liver Huke of the 

 sheep passes has not been fully traced, but the life-history of 

 Distoina inilitare, another species of the same genus, which in- 

 habits the intestines of water-birds, has been nearly completely 

 traced and from it we may, with wliat we know of the life 

 of the liver fluke, form a somewhat correct idea of the history 

 of its transformations. 



"This species, as stated, in its perfect or mature state, re- 

 sides in the intestines of certain water-birds. The ova or 

 spore-like eggs which it produces are few, some eight or ten in 

 number. From each egg issues a ciliated larva, which still 

 retains something of the character of an egg, although active, 

 as there is an outer envelope in wliich is the n'al animal, oi' in 

 whicli it developes, its history at this point of its life being yet 

 imperfectly known. From this egg-like larva i)roceeils the 

 secontl larva form, whieh is known as a Redia. Its mode of 

 development in this form is not fully known. It is now found 

 attached usually to the body of some water-snail ( Paludind), 

 the cilia of the first laiva having now disappeared. When the 



