88
Oesophagostomum radiatum
immature adult. Walker raises the questions whether the eggs are laid in
the intestine of the host or after the worm has been passed in the faeces;
whether they develop inside the intestine or outside ; whether there is a
free -swimming larva and whether another host is necessary. The early develop-
ment and the first-stage and infective larvæ are described, the latter having
been observed to have a filiform tail and a zigzag intestinal lumen. ' The
larval development of O. apiostomum, therefore, is strikingly similar to and
wholly comparable with the development of Ankylostoma duodenale, which is
perhaps to be expected from the somewhat near relationship of the two worms.
From this similarity in the development of the larva one would expect by ana-
logy that the method of entrance of the larva into the body of the host would
also be similar'.
Veglia [ 1923 ] published his results on Oesophagostomum columbianum
in sheep, forming the most important work on the life-history of an oesopha¬
gostome. He distinguished five stages with four ecdyses, the third stage
being infective and the fifth the adult. The larvæ hatch out of the eggs in
seven to twenty hours, the first-stage larva lasts for nearly 24 hours
and the second-stage larva three days. The infective larvae normally
attack the large intestine, emerge from the nodules on the sixth day after
ingestion, complete the fourth ecdysis by the 26th day and grow into
the adult by the 30th day. Thus, the parasitic stages are developed ex-
clusively in the intestine and the larvae do not pursue a migratory course in
the blood-stream. He says ' the larvæ of Oesophagostomum exhibit the same
phenomenon of thigmotropism, heliotropism, geotropism, and hydrotropism,
already described for those of Haemonchus contortus. The resistance of the
former to external conditions in the open also shows no marked difference to
that previously reported for the latter '.
Of the development of the free-living larvæ of Oesophagostomum dentatum
from the pig, Goodey [ 1924] gave a summarized description, with no indica-
tion of the rate of growth. In their morphology, the larvæ agree with those
of O. columbianum, and in their reactions to the surroundings they have been
shown to be positively geotropic, resistant to desiccation for one or two days
and exhibiting no marked positive thermotropism.
The same author [ 1926 ] made a study of the parasitic stages of the para-
site inside the pig, and records the interesting observation that no nodules
in the intestine were seen by him, even in heavy infections. Descriptions
of the early third-stage and the fourth-stage larvæ, including the metamor-
phosis into the adult with special reference to the buccal capsule and sexual
organs, are given.
A report by Veglia [ 1928 ] on Oesophagostomiasis in sheep due to Oeso-
phagostomum columbianum was an exposition of the method of artificial
infection, cultivation of larvæ and an analysis of the disease. The life of
the worms in the host has been judged to last 20 months. The symptoma-
tology and therapy of the disease form the larger portion of the paper.
Spindler [ 1933 ] obtained infective larvæ of O. longicaudum by culturing
eggs on moist sterile soil for five to seven days, and infected pigs with them.
Their resemblance to those of O. dentatum is recorded by him. The fourth-
stage larvæ and the adult are described in detail, much emphasis being laid