324 
Strongylids of Horse 
The cysts in the wall of the caecum appeared of a bright, blood-red colour, 
each on being opened was found to contain a cavity, filled with blood, in 
which the larvae lay coiled. These larvae were also blood-red in colour; they 
varied in length from 6 mm. to 11 mm., the larger forms being also found 
free in the cavity of the caecum. 
The smallest larvae (6-7 mm. in length) differ markedly in their structure 
from the adult worms; the characteristic leaf-crowns and the oral capsule are 
not yet developed, the latter being replaced by a provisional mouth-capsule 
Fig. 5. Cylicostomum insigne Boulenger. Lateral views of anterior extremity of larval forms. 
A. Young larva, 6 mm. in length. B. Older larva, 11 mm. in length, x 200. 
of a different shape. The cavity of this capsule is narrowed anteriorly and 
posteriorly, its walls are thick and in optical section (Text-fig. 5 A) appear to 
taper at the two extremities. An oesophageal funnel is present from the dorsal 
side of which a pointed tooth projects into the cavity of the mouth-capsule. 
This tooth is well adapted for piercing the tissues, there can be little doubt 
that the larvae when present in large numbers are capable of inflicting serious 
injury on their hosts. 
At this stage the tail of the larva is narrow and pointed, there is as yet no 
differentiation into the two sexes. 
