40
Scientific Memoirs by
G. M. G.), and a well-formed, chitinous, cup-shaped oral aperture ; also six cephalic
and at the neck two papillæ, and a well defined fold."
I am inclined to believe that the observation as to the absence of digestive
apparatus is erroneous. I have watched many embryos of this species as they
issued from the egg, and have always been able to make out an already well-
developed digestive tract, with a double bulbar apparatus, even in those that
had but just wriggled out of the egg-shell. One often sees similar notices with
regard to other nematodes, and I have met with specimens where, at first sight,
I could make out no digestive organs, but by careful examination and the
use of suitable re-agents have always been able to prove my first impression to be
wrong. I believe most of these false observations arise from the unchecked
examination of balsam and glycerine mounted specimens, media which quite
obliterate fine details for thick specimens. They are best examined in water, and
the addition of a little suspended carmine to the water containing living speci-
mens will often show up the intestine. Failing this, the addition of a small pro-
portion of alcohol may be tried, or tear up a specimen with needles and stain with
borax carmine or picrocarmine. Without previous slitting or tearing, it is useless
to attempt to stain, as the impermeable chitinous cuticle entirely prevents the
stain from reaching the organs which it is desired to differentiate.
If the newly-hatched embryos have well developed digestive organs, it is a
fortiori, highly improbable that the much older encysted worms should have
these organs undeveloped, and I certainly have not met with any such.
His minimum measurement too appears to me curiously small. Embryos
fresh from the egg are larger than this.
The adult worms are found exclusively in the large intestine, and, so far as
I have seen, their favourite residence is some distance along the colon, but few,
as a rule, being found in the cœcum. The only ovine parasite they are likely,to
be mistaken for is Dochmus hypostomus Diesing, which, being about the same
size, and having the same habitat, is easily confused with it. D. hypostomus,
however, averages larger, in all dimensions, and may be further distinguished by
the more distinctly globular form of the head, which forms quite a knob at the end
of its body, and the form of the male bursa, which has an elongated, instead of
a transversely oval, outline.
I am doubtful whether our species has the habit of blood-sucking. I have
not yet met with them actually hanging on to the mucous membrane ; but this
may be owing to my never having examined a warm carcase. However that
may be, it may be considered certain that the harm they do as adults is small
compared with the mischief effected during their stage of encystment.
From the fact that the number of free adults found is generally small in
comparison with that of the tumours, it is probable that the period of their stay
within the intestine is comparatively short, and that they rapidly discharge their
generative products, and are then extruded with the dung.
The harm done by the encysted worms, on the other hand, must be ex-