28 
Fig. 7. a, First-stage larva; b, anterior end of late 
first-stage larva, c, first-stage larva in process of molting, 
showing loosened cuticle at anterior and posterior ends. 
Fourth-Stage larvae were first seen on the 
fifth day, although some third-stage larvae 
were still present until the seventh day. The 
reproductive organs developed rapidly dur- 
ing this period: the vulva of the female was 
apparent on the seventh day and the develop- 
ing short spicule of the male on the ninth day. 
A separate mesostom and protostom had 
begun to form by the thirteenth day. For most 
larvae the final molt occurred about the 
PACIFIC SCIENCE, Vol. V, January, 1951 
twenty-first day, and young adults were pres- 
ent on the twenty-third day. Embryonated 
eggs were first observed in the crop contents 
of a chicken on the thirty-second day. Egg 
laying apparently began between the thir- 
tieth day, when the previous negative ex- 
amination was made, and the thirty-second 
day. 
DESCRIPTION OF THE LARVAL STAGES 
First-stage larvae 
Because of their small size and poor de- 
velopment the various structures of the first- 
stage larvae were discerned only with dif- 
ficulty. The newly hatched larvae were long 
and slender, being somewhat attenuated at 
the anterior and posterior ends. The anterior 
end was rather blunt and the relatively Jong 
tail was acute. In the later period of this stage, 
the tail shortened considerably, the relative 
growth in width exceeded the growth in 
length, and the body assumed a more-or-less 
club-shaped appearance because of the en- 
largement of the several large rectal cells. The 
maximum size observed in this stage was a 
length of 339m ^.nd a width of 24.9m- (See 
Table 5. Tables 5, 6, 7, and 8 show detailed 
measurements of a single typical larva for 
each of the days recorded. When size varia- 
tions among the larvae on a particular day 
were significant, detailed measurements of 
more than one larva are given. When the sex 
of the larvae could be readily determined, 
measurements of both male and female larvae 
for a particular day were made.) 
The cuticle was very thin and transparent 
and bore fine transverse striations. No papillae 
were apparent in this stage. 
The oral opening was surrounded by a ring 
of highly refractile material. The transparent 
esophagus extended approximately one-third 
the length of the body and terminated as a 
large spherical bulb, possessing what ap- 
peared to be an esophageal valve. The intes- 
tine consisted of a number of rather large, ill- 
defined cells containing numerous large vacu- 
oles of lipid-like material. The ventral anal 
