146 
Nematodirus filicollis Rud. 
weeks were present in such numbers in this position as to appear to 
the naked eye as a whitish deposit covering the whole of the inner 
surface of the vertical walls. When the dishes were removed from the 
moist chamber the larvae did not return to the damp faecal mass at 
the bottom, but dried and adhered to the walls as the moisture 
evaporated. The larvae also ascended blades of grass and seedlings 
placed in the dishes. 
Ransom has already pointed out in the case of Haemonchus contortus 
(1906) how this upward migration of the ensheathed larvae is connected 
with a method of infection most peculiarly adapted to the food habits 
of sheep and other herbivorous animals; the similar migratory instincts 
of the larvae of Nematodirus filicollis suggest that these reach the 
alimentary canals of their hosts in the same manner. 
The ensheathed Nematodirus larvae are evidently able to maintain 
their existence in water for a considerable period, I have kept specimens 
in small watch-glasses for over eleven months. 
Perhaps the most striking feature in the biology of the larvae is 
their power to withstand desiccation for long periods. This phenomenon 
can be studied by allowing a drop of water containing larvae to evaporate 
on a glass slide; as the moisture of their surroundings becomes reduced 
the larvae contract somewhat within the sheaths and usually coil 
themselves into a spiral, the fhiid within the sheaths is still present 
for a short time after the water on the slide has completely evaporated, 
this however soon disappears and the larvae become much shrivelled, 
assume a glassy appearance and become extremely brittle. When 
remoistened the larvae quickly absorb water through their sheaths, 
regain their shape and gradually uncoil, the whole process often taking 
less than twenty minutes. 
• The larvae can in most cases endure repeated drying and 
remoistening and in one experiment I successfully dried and revived 
a number of individuals twelve times in six days. 
The Nematodirus larvae are able to withstand complete desiccation 
equally well whilst still within the egg-shell, this however only applies 
to the mature embryos which are already provided with sheaths. 
The maximum period for which the larvae can retain their vitality 
when subjected to complete desiccation was not ascertained, my experi¬ 
ments however showed that they can do so for a very long time. I will 
quote one interesting experiment in support of this statement. A small 
mass of faeces, known to contain numerous eggs enclosing mature 
larvae, was placed in a small open box on August 30th, 1913, and then 
