G-. H. F. Nuttall 
147 
Under certain conditions (specified in the foregoing table) hatching may 
be delayed up to 35 days. 
Capitis eggs hatched on the wrist at 32-35° C. in 5-9 days, mostly 
(60 %) in 7 days. When carried near the body at 30-35° C., in warm 
weather, they hatched in 6-10 days, mostly (68 %) in 7 days; under 
the same conditions, in slightly cooler weather, they hatched in 6-9 
days, mostly (61 %) in 7 days. The influence of slight variations in 
temperature is well brought out in the protocols (see p. 145). 
Development of the Larva in the Egg. 
The following description relates merely to the changes that can be 
observed ivith a low magnification. Certain details relating to histology 
will be considered elsewhere. The freshly laid egg, when viewed by 
transmitted light, appears almost transparent and faintly yellow; 
the contents fill the shell and are finely granular (Fig. 9, l). Assuming 
that an egg is placed at a temperature which allows of its development 
so that it hatches in six days, the following changes can be observed 
to take place through the egg-shell when the nit is viewed in a living 
condition: 
2nd day. Segmentation has begun. Round volk-masses of variable 
size are formed and their number increases; they are best seen by 
oblique illumination (Fig. 9, 2 and 3). 
3 rd day. Slightly opaque milky areas appear along one side and 
basally (4) and the limbs begin to form (5), the yolk masses fade and the 
body becomes defined, a clear space appearing basally in the shell. 
4 th day. The body and limbs become more clearly defined (Fig. 9, 6), 
the eyes become visible as two irregular pinkish antero-lateral spots. 
5th day. When closely viewed, periodic pumping movements of the 
pharynx are observable. The stigmata may be seen, the claws and 
eyes are darker. The egg as a whole appears more yellowish brown 
and the eyes reddish. There may be slight movements of the limbs 
(Fig. 9, 7). Occasionally bubbles may be seen in the fluid in which the 
larva floats; they at times escape upward along the venter of the larva 
and pass over its head toward the operculum. The shell shows shrink¬ 
age, there being two long shallow spoon-shaped depressions seen postero- 
laterally; this shrinkage is very different from the total collapse seen 
on the first and second day in sterile incubated eggs. 
6 th day. The shell appears more hollowed at the sides. The 
pharyngeal pumping movements are more frequent, and bubbles of 
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