C. L. Boulenger 
141 
and the embryo is approximately cylindrical in shape, except posteriorly 
where the body tapers to a long slender tail. 
The embryo at this stage performs continuous, although somewhat 
sluggish, movements within the egg-shell; its internal organisation is 
not visible, the whole of the body with the exception of a small 
spot at the cephalic extremity being filled with dark, yolk-like 
granules. 
During the second fortnight important changes take place, the 
opaque granules of reserve substances are slowly absorbed and the 
internal organisation of the embryo gradually revealed, the latter 
moreover undergoes two ecdyses before appearing in its final condition 
ready for liberation from the egg-shell. The mature embryo is quite 
transparent and appears highly refractive, it is enclosed in a tightly 
fitting sheath, the uncast skin derived from the second ecdysis, and is 
still surrounded by the shed skin from the first moult. The mature 
embryo is extremely lively at ordinary laboratory temperatures and is 
in continual motion within the egg-shell. 
The Hatching of the Embryos. 
For some time great difficulty was experienced in getting the embryos 
to hatch from the eggs, many mature eggs were kept for weeks in the 
laboratory without a single larva being freed, whilst in some cultures 
even after seven months more than 90 per cent, of the embryos were 
still unhatched although apparently healthy and moving actively within 
the egg-shells. 
Mr H. E. Hornby, who had made some observations on this species 
at the South-Eastern Agricultural College at Wye, informed me that he 
bad had the same difficulty in obtaining larvae from Nematodirus eggs 
kept in moist faecal cultures, but had been more successful with some 
cultures which had been dried for a short period. I therefore tried 
the effect of submitting some of my cultures to alternate desiccation 
and remoistening; this yielded somewhat better results, a few larvae 
hatching at each remoistening but still forming a very small per¬ 
centage. 
It is, of course, well known that the larvae of many Nematodes 
hatch only when the eggs are taken into the body of their host, this 
led me to try the effect of temperatures approximating to that of the 
blood on the mature eggs of Nematodirus filicollis. In an oven at a 
temperature of 38° C. the embryos with only few exceptions hatched 
