Nov. 1„ 1924 
Pre/parasitic Stages of the Cattle Hookworm 
453 
cultures, but also because of other 
factors probably present within the 
egg as well as in the surrounding 
medium. 
PREINFECTIYE LARVJE 
The first-stage larva exhibits lively 
movements, twisting its body in typical 
nematode fashion. Several first-stage 
larvae were kept under observation 
about seven hours, during which period 
they were incessantly active, moving 
about with vigorous flexures of the 
anterior portion of the body aided by 
the propelling movements of the long, 
slender tail. 
These larvae are commonly from 420 
to 450 ju long, or somewhat longer, by 
20 to 25 m wide. The first third of 
the body is the broadest, the remaining 
portion tapering gradually and ter¬ 
minating in a slender tail. Structurally, 
the organism is relatively simple, its 
most conspicuous organs being an 
alimentary canal consisting of an 
esophagus with a terminal bulb and a 
straight intestine (this being densely 
granular in contrast to the less granular 
esophageal region), and a genital 
primordium. 
About 24 hours after hatching, first- 
stage larvae became very sluggish, a 
physiological condition (lethargus) 
which precedes molting. Examina¬ 
tion of such sluggish larvae with 
high magnification generally showed 
a separation of the cuticle in the 
cephalic extremity, revealing a newly 
formed cuticle underneath the old 
one. 
The span of life of the second-stage 
larvae is comparatively brief, since 18 
hours after the first lethargus was 
observed the second lethargus was found 
to be in progress. The second-stage 
larva shows a slight increase in size 
(490 by 25 n) and is less coarsely 
granular than the first-stage larva. 
Before its quiescent stage preparatory 
to the final molt it shows moderate 
activity, less marked, however, than 
that of the first-stage larva. 
Although in a 6-day-old culture 
several quiescent larvae undergoing the 
final molt were found, third-stage 
larvae were generally not observed be¬ 
fore the eighth day after making the 
culture. The second lethargus lasts at 
least 24 hours. 
The duration of the preinfective 
stages in the life of the larvae may be 
increased by subjecting them to low 
temperatures, which retard their de¬ 
velopment. Thus first-stage larvae were 
prevented from further development 
for a period of 10 days by being kept 
99186—25f-3 
in water in a refrigerator at a tempera¬ 
ture of 8° C. While a number of larvae 
degenerated during that period, others 
were still alive and showed no changes 
of structure or other evidence of having 
molted. Meanwhile larvae from the 
same lot at room temperature under- 
Fig. 2.—Outline drawing of infective larva from solid 
culture medium showing protective sheath 
went their normal course of develop¬ 
ment. 
INFECTIVE LARVAE 
In rich 8-day-old cultures third-stage 
larvae were found in abundance. These 
organisms are readily recognized by 
their greater transparency, which in- 
