110 
The Rot in Sheep. 
nervous system, but we certainly see no reason to doubt Mehlis' 
description, and therefore cannot say with Kuchenmeister that it 
" is wanting." 
Having now 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, are only so in their highest 
stage of development. To reach this they undergo a series of 
successive metamorphoses, 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 circumstance which 
explains many of the facts practically known to agriculturists 
and others respecting 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 those through which the 
Distoma hepaticum really passes from the ovum to the perfect 
entozoon must be somewhat incomplete, because all of them have 
not as yet been 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 immense. This 
difficulty is not a little increased by the circumstance that when 
many of these forms are existing in water as infusoria we fail to 
identify them with the particular entozoon to which they belong. 
Upon the correct solution of the problem, however, hangs our 
chief hope of affording security to animals against those entozoa 
which undergo such transformations. 
The family of flukes alone is a very numerous one, and has 
been estimated by some naturalists at from four to five hundred, 
all of which are thought 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 Distoma hepaticum, and that helminthologists are 
enabled to speak with confidence upon some of the transforma- 
tions it undergoes ; and not only so, but to give practical effect 
to this knowledge by advising flockmasters how to protect their 
sheep in a great measure from its attacks. 
* While these pages \vere passing through the press our attention was directed 
to a 'very excellent paper on the anatomy of the Distoma hepaticum, in the ' Intel- 
lectual Observer,' by Dr. T. Spencer Cobbold, Lecturer on Comparative Anatomy 
at the Middlesex Hospital, who, we are glad to see, agrees in veiy many particulars 
with ourselves. 
