C. L. Boulenger 
325 
In slightly older larvae a series of cavities can be seen developing behind 
the provisional month-capsule, these are the rudiments of the adult oral 
capsule (Text-fig. 5), the chitinous walls of which soon also make their appear¬ 
ance. A little later the first signs of an approaching ecdysis are noted, the 
cuticle of the larva appearing double. 
In the largest larvae (11 mm. long) both provisional and adult mouth- 
capsules are quite distinct (Text-fig. 5 B), the adult oesophageal funnel has 
also made its appearance and is seen to surround the provisional funnel. At 
this stage differentiation of the sexes has also begun and in the males the 
bursa can be distinctly traced, still however enclosed within the cuticle of the 
pointed larval tail. 
When the final ecdysis occurs the larval cuticle is shed, carrying away with 
it the provisional mouth-capsule together with the funnel and its tooth. 
The adult worms met with in the posterior part of the colon are also blood- 
' red, but of not quite so bright a colour as the larvae. I have little to add to 
my original description except with regard to the structure of the oesophageal 
funnel. 
In preserved specimens, killed by immersion in hot alcohol, the whole 
body is fixed in an extended condition, in this state the anterior region of the 
oesophagus appears narrow, with thick muscular walls surrounding a small 
cavity scarcely sufficiently developed to call an oesophageal funnel (Boulenger, 
1917, Fig. 3 a). Observation of the living worms has shown me that during hfe 
the anterior division of the oesophagus is capable of expansion and contraction 
to an extraordinary degree, so that when the muscles of this region are fully 
contracted its cavity appears correspondingly expanded, forming a large, wide 
funnel which can be seen to be lined by a delicate membrane, evidently con¬ 
tinuous with that covering the inner surface of the mouth-capsule. 
In this contracted condition the anterior part of the oesophagus appears 
very broad and is sharply marked off from the rest of the organ by a narrow 
“neck.” This is the condition met with in the worms, obtained from a zebra 
in E. Africa, which were described by me under the name C. zebrae (1920, 
Figs. 3 and 4), these now appear to be much contracted specimens of C. insigne. 
I was able to obtain a similar appearance in the latter species by allowing 
specimens to die in cold, weak alcohol. 
C. insigne is now known from Europe, Asia, E. Africa (in the zebra) and 
N. America (Ransom and Hadwen, 1918). 
REFERENCES. 
Boulenger, C. L. (1916). Sclerostome Parasites of the Horse in England. I. The Genera 
Triodontophorus and Oesophagodontus. Parasitology, vm. 420. 
- (1917). IT. New species of the Genus Cylichnostomum. Parasitology, ix. 203. 
-(1920). Sclerostomes of the Donkey in Zanzibar and East Africa. Parasitology, xn. 27. 
- (1920 a). On some Nematode Parasites of the Zebra. Parasitology, xn. 98. 
Giles, G. M. (1892). On a new Sclerostome from the Large Intestine of Mules. Sci. Mem. 
Med. Officers Army of India, vn. 25. 
