The Hot in Sheep. 



41» 



description, and therefore cannot coincide with the statement of 

 Kiichenmeister that it " is wanting." 



Having explained the general structure of the entozoon as 

 fully as present circumstances seem to require, we pass on to 

 speak of its natural history and development. 



Natural History of the Distoma hepaticum. 



The Distoma belongs to that class of creatures which, although 

 parasitic to mammalian animals in particular, are only so in 

 their matured condition. To reach this they undergo pro- 

 gressive development, out of the body of the animal which 

 they ultimately inhabit. The liver-fluke, while passing through 

 some of its transformations, is met with in rivulets, ponds, 

 stagnant waters, wet pastures, and allied situations — a circum- 

 stance which explains many facts which are practically 

 known to agriculturists respecting the occurrence of the rot in 

 sheep. 



Notwithstanding the rapid advances made by science within 

 the last few years in unravelling many of the singular metamor- 

 phoses of entozoa, our description of the changes through which 

 the Distoma hepaticum passes from the ovum to the perfect 

 entozoon must be somewhat incomplete, because some of them 

 as yet have to be fully traced out. A far greater difficulty than 

 might be supposed belongs to investigations of this kind, and 

 the time and patience required for the purpose are indeed very 

 great. This difficulty is not a little increased by the circum- 

 stance that when several infusorial forms are present in water, 

 we may fail to identify some of them with the particular ento- 

 zoon to which they are related. Upon the correct solution of a 

 problem like this, however, depends the chief hope of affording 

 security to animals against an attack of those entozoa which 

 undergo such transformations. 



The family of flukes is a very numerous one, and has been 

 estimated by some naturalists at from four to five hundred, 

 all of which are supposed to pass through allied metamorphoses. 

 As flukes they are parasitic to mammals, birds, fishes, reptiles, 

 and even non-vertebrate creatures. With facts like these to 

 grapple with, the only wonder is that so much is really known 

 about the development of the Distoma hepaticum, and that 

 helminthologists are enabled to speak with confidence upon 

 most of the transformations it undergoes ; and not only so, 

 but to give practical effect to this knowledge by advising Hoek- 

 masters how to protect their sheep in a great measure from its 

 attacks. 



Ova, — Elsewhere it has been shown that the number of ova 



E 



