1896. NOTES AND COMMENTS. 371 



a page of the Journal of Geology ; while an equivalent weight of 

 Natural Science would contain far more than twice as much matter. 

 We use our own Journal for comparison merely because it is the 

 nearest to our hands, and doubtless our valued contemporary makes 

 up for this discrepancy by the greater weight of its words. 



The Liver Fluke. 



Since the classical researches of A. P. Thomas on this parasite 

 of the sheep, all naturalists have known that its larval stages, under 

 the peculiar shapes known as vedia and cercaria, are developed in the 

 STidiiX Limncea tmncatnla, and that the cercaria, eventually escaping from 

 the snail, encysts itself either on a water-plant or on blades of grass, 

 where it is readily eaten by sheep. Some members of the Field 

 Naturalists' Club of Victoria have recently obtained from the fresh- 

 water snail, Isidora tentiistriaia, large numbers of redia and cercaria 

 similar in form to those found in LinmcBa truncahda. They have also 

 been found in Isidora texturata, Ancylus tasmanicns, and a species of 

 Planorhis. Other forms of cercaria have been detected in Segmentina 

 victoricB, Planorhis gilherti, Isidora gibbosa, var. fnsiformis, and Liinnaa 

 lessoni. These may of course belong to some other species than Fasciola 

 (or Distomuvi) hepatica. 



"What causes surprise," says the Victorian Naturalist, "is the 

 wonderful amount of ingenuity which the ciliated embryo fluke employs 

 in obtaining admission to the pulmonary chamber of such snails as 

 Planorhis and Ancylus. The former takes the shape of a disc only ^ in. 

 thick and ^ in. across, whilst the latter can scarcely measure half 

 that size. Our special climatic conditions evidently arouse desire in 

 the embryo to widen its choice in the matter of suitable hosts. This 

 fact unfortunately multiplies the chances of the increase of liuke, for 

 whilst only one species of one genus favours the transmission of the 

 pest in Europe, at least three or four different genera must be credited 

 to Australia." 



As stated above, it is supposed that sheep eat the fluke in its 

 encysted form upon grass or water-weed. The Rev. W. Fielder has, 

 however, observed that cysts are formed actually within the snails 

 Planorhis diXid Ancylus, molluscs which, from their small size, may easily 

 be swallowed by the sheep when drinking. Mr. W. McCaw has also 

 noted cysts within Isidora tenuistriata. Possibly, as the Victorian 

 Naturalist suggests, this last stage of larval life has also been influenced 

 by the special chmatic conditions. Anyway, the danger to sheep is 

 still further increased. 



" Remember Mitchelstown ! " 



This continues to be the watchword of the green-coated Irish 



Naturalist (we refer, of course, to our estimable contemporary, so ably 



conducted by G. H. Carpenter and R. Lloyd Praeger, not to any 



individual), and an excellent watchword it is. In a note headed 



