140 
Nematodirus filicollis Rud. 
seemed not to require much air and developed well in solid watch- 
glasses with sealed covers or in small corked tubes. 
The presence or absence of daylight has little or no effect on the 
development, eggs developing equally well whether exposed to light or 
kept in a dark chamber. 
A certain amount of moisture was found to be essential, in the earlier 
stages of development the eggs were invariably killed by desiccation; 
excess of moisture is not harmful to the cultures, for, as already 
mentioned, development proceeds perfectly well in pure water. 
The rate of development of the eggs, always slow as compared 
with other Strongylids, is very strongly influenced by temperature 
conditions which are certainly of the greatest importance. Extensive 
series of experiments concerning this factor could unfortunately not be 
made, cultures were however kept at a number of different temperatures 
and the general effects of these conditions ascertained. 
The best results were obtained at temperatures between 19° C. and 
27° C., i.e. warm summer temperatures, under these conditions eggs 
were found to contain mature larvae ready to hatch 24-28 days after 
leaving the body of the host. At ordinary laboratory temperatures 
(13°-15° C.) development proceeded more slowly and with less regularity, 
eggs often taking 5-6 weeks to produce mature larvae. At low tem¬ 
peratures development'is suspended, freezing kills the eggs in their 
early stages. 
Several cultures were kept in an incubator at a temperature of 38° C., 
under these conditions the eggs developed rapidly as far as the morula 
stage, after which the majority died; no mature embryos were formed, 
thus indicating that complete development cannot take place at the 
blood temperature of the host and that eggs swallowed by sheep during 
the earlier stages would not survive. 
As already mentioned the eggs usually contain 7-8 cells when laid, 
they do not develop further until they leave the body of the host. In 
water or moist faeces the development of the embryo continues and 
is of quite the normal type, resembling that of other Nematode worms. 
Under favourable temperature conditions the morula stage is reached 
in 3-4 days and is soon followed by the characteristic “tadpole” stage, 
in which the embryo is flexed and considerably thickened at the anterior 
extremity. The first movements of the embryo now become apparent, 
the latter continues elongating and by the end of the first fortnight 
has reached a length of approximately five times that of the egg in which 
it lies coiled; the thickening at the anterior extremity has disappeared 
