ROT IN SHEEP. 
281 
specific malady. We come now to inquire a little into 
the natural history of the distoma, that we may see what 
light it will throw on the nature and progress of the disease, 
and upon the means at our disposal for preventing or curing 
the affection. It is self-evident that if a disease depends upon 
a special entozoon, if we are thoroughly acquainted with the 
natural history of the creature, and if by means of that know¬ 
ledge we can destroy or get rid of it, we shall thus be able 
to remove its effects. Now, without unnecessarily occupying 
time, let me say that the diagram shows dissections of the ento- 
zoon, more particularly with regard to its nutritive and gene¬ 
rative systems. You see that the sucking disc, to which I before 
directed your attention, is in reality a true mouth with which 
the creature takes in the bile with which it is surrounded in 
the biliary ducts ; and that this bile passes down through a sys¬ 
tem of vessels which are in reality assimilative vessels, and con¬ 
sequently may be regarded as nutritive. You observe there 
is a peculiarity with regard to the nutritive system. We 
see an entrance for the material by which the life of the crea¬ 
ture is maintained ; but we see no excretory organ—we cannot 
perceive that any feculent matter is thrown out as such from 
the hinder part or the sides of the entozoon. Strictly speak¬ 
ing, then, this is really an organ by which the creature receives 
into its system that which it requires for its growth, and by 
which it also rejects from its system that which is not needed. 
And here let me say, that although there are many works upon 
the anatomy of the fluke, containing very nice drawings or en¬ 
gravings—though Professor Owen gives an engraving of the 
creature in this work on the Invertebrata, and Rvmer Jones 
another in his work on the animal kingdom—in short, though 
therearetwenty or more representations by as many individuals, 
there is really none that can be depended upon as being per¬ 
fectly correct. I say it advisedly, because I have been engaged 
in investigations with regard to the anatomy and natural history 
of this creature for eight or nine years, taking up the subject 
from time to time, and working at it occasionally for days to¬ 
gether ; and it is only very recently that I have been enabled to 
satisfy myself as to some intricate points of its structure. I have 
seen these animals, when taken fresh from a slain sheep, and 
placed in warm water, eject the biliary matter again and again 
from the oral opening, which thus, as I have said, performs 
the office of an excretory organ as well as one by which the 
creature receives its nourishment. The nutritive svstem has 
really nothing whatever to do, or rather indirect communi¬ 
cation, with the generative system. The great point of interest, 
however, is the system of generation, which, when we come 
xxxiv. 21 
