C. L. Boulenger 
149 
The above experiments show that whilst at low temperatures the 
larvae of Nematodirus filicollis are occasionally able to complete their 
moults under certain somewhat abnormal conditions—they normally 
do so when subjected to a temperature of 38° C.—we may assume 
therefore that they would behave in a similar manner when taken 
into the body of a sheep or other host. 
Structure of the “ Exsheathed” Larva. 
Whilst retained within the sheaths the larvae of the third stage 
undergo no further development, and just after the completion of the 
second ecdysis show practically the same structure as those described 
on page 143 ; in most individuals however the food granules and vacuoles 
have almost entirely disappeared from the eight intestinal cells, revealing 
the nuclei as spherical bodies of a rather lighter colour than the proto¬ 
plasm surrounding them. 
Fig. 3. Genital rudiment and adjacent parts of body of larva fifteen days after completion 
of the second ecdysis. g. genital rudiment, i. intestine, n. nucleus of intestinal 
cell, x 750. 
In their behaviour these larvae differ markedly from those in the 
ensheathed stage, they have lost their agility of movement and at 
laboratory temperatures are exceedingly sluggish, often remaining 
motionless for hours. They show no tendency to climb vertical 
surfaces. 
In water or cultures of faeces the “exsheathed” larvae usually die 
within a few days, I however succeeded in keeping a few individuals 
for fifteen days in an oven at 38° C. These larvae showed little change 
except in the structure of the intestine and genital rudiment. 
By the fifteenth day the number of intestinal cells had increased 
considerably and fourteen nuclei could be counted; the cell limits were 
at this stage scarcely discernible and moreover the intestine now showed 
a distinct lumen. 
Parasitology vra 
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