454 
Journal of Agricultural Research 
Vol. XXIX, No. 9 
creases as they are kept alive in 
cultures. The earlier-stage coarser 
granules practically disappear and the 
larvae also retract within the shells, 
showing quite distinctly the protective 
sheath, which is usually wrinkled (fig. 2). 
The infective larvae are generally 
from 500 to 540 m long by 20 to 27 m 
wide, although infective larvae slightly 
less than 500 m long were found on several 
occasions. The distance from the ce¬ 
phalic extremity to the base of the 
esophagus was found to vary from 125 
to 145 m- The diameter of the esoph¬ 
agus at the base is 10m- The nerve 
ring has a diameter of 5 m and is usually 
situated 60 m from the cephalic ex¬ 
tremity. In one speci¬ 
men the distance was 
found to be 78m, while 
in another specimen it 
was only 50m- The dis¬ 
tance from the anterior 
extremity to the genital 
primordium is slightly 
in excess of 200 m- The 
genital primordium is 
10m long by 5m wide. 
The tail corresponds 
roughly to the terminal 
sixth of the total body 
length (fig. 4). 
Third-stage 1 a r v ae 
obtained from solid 
cultures have only the 
protective sheath, the 
first cuticle having been 
discarded. Third-stage 
larvae obtained from 
liquid cultures almost 
invariably show two 
sheaths, indicating that 
the first as well as the 
second sheath has been 
retained (fig. 3). This 
observation was veri¬ 
fied repeatedly in liquid 
cultures made from 
different lots of worms. 
The first cuticle (first 
molt) is generally rigid, 
whereas the second 
cuticle (protective 
sheath) is 
flexible 
and is 
often 
wrinkled. 
Larvae 
with two 
sheaths 
from 
Fig. 3—Outline drawing of infective P11 i 
larva from liquid culture medium 1 4 UiU CLA1 
showing two sheaths tures were 
kept 
under observation in cover-glass prep¬ 
arations, and it was noted that as the 
slide 
that 
i/io mm. 
nr? 
became almost dry certain larvae 
were in contact with some solid 
object discarded the first 
sheath. This observation 
was repeated a number of 
times and indicates that 
contact with a solid object 
is necessary to exsheath- 
ej. and also probably 
that a liquid medium is 
inimical to the completion 
of the ecdysis. According 
to Augustine (1), the first 
ecdysis in Ancylostoma 
duodenale is due to the fact 
that the larva has increased 
in size considerably and 
thus bursts the tightly sur¬ 
rounding sheath. The 
slight difference in size 
between first- and second- 
fntr stage larvae of Bustomwn 
phlebotomum renders other 
mechanical stimuli neces- 
y.o. ary for the completion of 
®he first ecdysis, and in 
%e absence of these stimuli 
Jhe first cuticle is retained, 
t 
BEHAVIOR OF INFEC¬ 
TIVE LARVAE 
GENERAL BEHAVIOR 
As observed in liquid- 
culture dishes and in hang¬ 
ing-drop preparations, in¬ 
fective larvae show but a 
moderate degree of activity 
at room temperature. 
Periods of activity and 
rest alternate, and while 
at rest the larva is either 
straight and 
rigid or some¬ 
what coiled 
and rigid. The 
protective 
sheath is gen¬ 
erally visible, 
Fig. 4.—Infective larva, oes., because the 
oesophagus; n.r.,nerve ring; hnrlv aIwavs 
sh., sheath; int., intestine; Doa y ls aiwaj S 
g. p., genital primordium more or less 
retracted with¬ 
in the sheath. Quiescent third-stage 
larvae usually become active when 
disturbed. A transfer from a culture 
dish to a slide stimulates them to 
activity involving rapid movements, 
which gradually become less intense 
and ultimately cease entirely. 
On slide preparations it was noted 
that the larvae commonly exhibit a 
tendency to come to rest when in con¬ 
tact with some solid object such as 
d4bris carried over from the culture 
medium. Larvae with the anterior 
