J. Johnstone 
377 
some slight variation in the arrangement of the hooks when the larva 
and adult worm are compared, but as a rule there is a great constancy 
in mature individuals. In comparing these drawings with actual 
specimens one must remember that quite a different appearance will be 
presented according to the way in which the proboscis lies since the 
hooks and spines in each oblique series differ from each other. One 
cannot slit up the proboscis and spread it out on the flat; and since it 
is necessary to focus down to the level of each hook it follows that those 
at the margins of the proboscis must be foreshortened. I have not 
been able to disintegrate the proboscis by maceration, or by treatment 
by alkalies: what happens in the latter method of treatment is the 
solution of the spines, and the shrivelling up of the sheath. 
The hooks and spines are arranged either as a continuous spiral 
runriing round the proboscis, or as a series of obliquely running rows— 
I have been unable to determine which arrangement is the actual one. 
They must he repeated from base to tip of the proboscis with great 
exactness since one always finds the same kind of hooks at the margins 
throughout a considerable part of a proboscis. There are five different 
kinds of hooks and spines which I letter as follows—the lettering being 
similar to that of the figures on PI. XX. 
A. Large, broad, sharply pointed hooks with slipper-shaped bases. 
These hooks are remarkably constant in size and shape and measure 
about 0 06 mm. from the perpendicular through the tip to the perpen¬ 
dicular through the other extremity of the base. There are two of 
these hooks in each series, and they lie adjacent to each other. 
B. Long, relatively narrow, curved spines with small expanded 
bases. They are nearly straight for the greater part of their lengths 
but are sharply recurved at the tips. Fig. B in the Plate represents 
the extreme degree of curvature, usually the hook is less sharply 
curved. The length is about 0'04 to 0‘05 mm. measured as in the 
figure. There are two of these hooks in each series, one adjacent to 
each of the large hooks A. 
C. Relatively long spines with slender sharp tips, and blunted 
projections near the bases. The latter are very small. Tfie apical part 
is bent round nearly at a right angle to the basal part and is sometimes 
recurved in the opposite direction. The projection near the base may 
function like the barb in a fish-hook. The length of these hooks is 
about 0‘04 mm. and there are two in each series, one being adjacent to 
each of the spines B. 
Parasitology iv 
•25 
