349 
Extracts from British and Foreign Journals. 
ROYAL AGRICULTURAL SOCIETY. 
LECTURE ON THE NATURE AND CAUSES OF THE DISEASE 
KNOWN AS ROT IN SHEEP. 
By Professor J. B. Simonds. 
[Continuedfrom p, 283.) 
I have said that the liver fluke passes through a series of 
metamorphoses, or what have been designated alternations of 
generations; and perhaps I may be allowed to explain the 
difference made by scientific men between the two. In alter¬ 
nations of generations we have an animal which produces its 
ova in the ordinary manner; the young, however, which 
come from the ova are dissimilar altogether from their parent, 
but are nevertheless capable of a new system of generation, 
and the creatures which they propagate as a second or a 
third step, pass back to the original form of the parent. 
Ordinary metamorphosis is a different thing. Take the case 
of a bed-flea, for example, that being the first that occurs to 
me. The animal produces ova; these ova produce larvae; 
the generative system becomes developed, but the larva does 
not propagate. It attains its full size, and then becomes a 
chrysalis or pupa; subsequently the perfect flea is formed 
out of the chrysalis, and it is in that state only that the 
generative system reaches its highest order of development. 
There is no alternation of generation, in other words there 
is no generation from the larva or pupa. Now this is a part 
of the natural history of the fluke, which, although it has 
received the greatest amount of attention from investigators 
on the continent and in England for some time past, is still 
to a considerable extent shrouded in mystery. 
We have satisfied ourselves, as I have before explained, 
that we have from out of fluke eggs living creatures ex¬ 
ceedingly small, much smaller than the egg itself, and that 
these do not immediately develop into flukes, but go through 
a series of alternations of generations. Now what I am going 
to explain will only allow of an analogy with regard to the 
distoma. Before explaining it, however, let me say that we 
believe that each of the fluke eggs contains a number of 
moving, ciliated cells, which are more or less round in form, 
and that these are set at liberty and pass into water, for 
