134 
Nematodirus filicollis Rucl. 
These round-worms have in recent years formed the subject of careful 
study by a number of investigators, the latter, however, have confined 
themselves largely to the systematic and anatomical features of the 
adult individuals, the larval forms and life histories generally receiving 
only brief -and occasional notice. Thus of the Strongylidae inhabiting 
the sheep’s alimentary canal and to which family the majority of the 
most injurious Nematodes belong, there is only a single species, Haemon- 
chus contortus, whose life history has received adequate attention 
during the last few years. Our knowledge of the development of the 
other forms is very incomplete and in most cases confined to scanty 
descriptions of isolated larval stages. 
The presence of Haemonchus contortus, the well-known “ Twisted 
Wireworm,” in the fourth stomach of sheep has been proved to be 
responsible for very serious losses among flocks, both in this country 
and abroad; opinions vary, however, as to the amount of damage 
caused by the other common Strongylid round-worms of the alimentary 
tract, although most agree that when occurring in large numbers the 
majority are capable of inflicting very serious, if not fatal injuries, 
whilst lighter infections may lead to weakness and loss of condition, 
especially among lambs and yearlings. 
Vermifuges and other medicinal remedies have not proved entirely 
satisfactory, and of late years the efforts of agriculturists have been 
directed towards preventing or reducing the infection by these parasites. 
Effective prophylactic measures against Nematodes cannot however be 
devised until a thorough knowledge of their life histories is obtained 
and this should include the biology as well as the anatomy of the various 
larval forms. 
It was with the intention of filling up one of the numerous gaps in 
our knowledge of sheep Nematodes that the observations recorded here 
were undertaken. Nematodirus filicollis was selected for study for a 
number of reasons: (a) in spite of the few records of its occurrence it 
proved to be a very common species in different parts of England, 
(b) our knowledge of its life history is confined to short and incomplete 
descriptions of the newly-hatched larva, and (c) the ease with which 
material could be obtained and the large size of the eggs in this species 
make it a very convenient form for study. 
My observations on the parasite were commenced in August, 1913, 
at the South-Eastern Agricultural College at Wye in Kent 1 , the greater 
1 I wish to take this opportunity of expressing my indebtedness to Mr H. E. Hornby 
of this institution for placing a quantity of Nematodirus material at my disposal; 
