Oxyspirura mansoni — -Schwabe ■ 
were each embedded in a multinucleate lateral 
line 50 /I in width. 
The nervous system appeared much the 
same_as in the second-stage larvae. 
The sexes could be distinguished readily 
in the third stage. In the female the genital 
primordium could be seen attached to the 
ventral body wall approximately 650 /x from 
the posterior end. In the male the primordium 
was similarly situated but unattached. The 
primordium in both sexes measured approxi- 
mately 35 M by 14 /X in this stage and was 
composed of several cells. 
Fourth-stage larvae 
In general proportions the fourth-stage 
larvae differed little in appearance from those 
of the third stage. Early fourth-stage larvae 
measured about 10 mm. in length while those 
in the later portion of the stage measured 
from 12.8 to 14 mm. 
Fine transverse striations were evident in 
the transparent cuticle. The four sublateral 
papillae each measured approximately 4.6 ju 
in length. In addition^ by the twenty-first 
day, the two latero-caudal papillae had begun 
to form, and the preanal and postanal papil- 
lae of the males were evident. 
By the thirteenth day the separate pro- 
tostom and mesostom could be differentiated, 
and in the later part of the stage the buccal 
capsule appeared much the same as in the 
adult. 
The remainder of the alimentary tract 
showed little change from that of the third- 
stage larvae, the intestine being displaced 
somewhat to allow room for the developing 
reproductive organs. 
The lateral excretory canals were seen to 
terminate in the latero-caudal papillae in the 
late fourth-stage larvae. Other than this, the 
excretory system had apparently achieved its 
full development by the end of the third 
stage. 
The only additional development noted in 
the nervous system in the fourth stage was 
the appearance of two large dorsal and two 
33 
large ventral ganglion cells near the nerve 
ring. 
In the fourth-stage larvae the greatest de- 
velopment occurred in the reproductive sys- 
tem. By the fourth day the genital primord- 
ium in both sexes measured approximately 
214 ju in length and in the case of the female 
was attached to the ventral body wall. The 
point of attachment, which later became the 
vulva, was approximately 894 ^ from the 
posterior end. In the male the genital pri- 
mordium became a U-shaped tube with two 
terminal bulbous growing tips developing 
toward the posterior end. By the ninth day 
the short spicule of the male had begun to 
form and the vulva of the female was ap- 
parent, although it remained closed externally 
during the entire fourth stage. The repro- 
ductive tract, at least in the female, appeared 
almost complete by the thirteenth day. By 
the sixteenth day the long spicule of the 
male could be recognized. The male repro- 
ductive system was well formed by the 
twenty-first day; the ejaculatory duct could 
be seen to enter the ventral side of the rectum 
at its posterior terminus, the anal papillae 
were evident, and both spicules were well 
developed. 
Acknowledgments'. I wish to express my sincere 
appreciation to Dr. J. E. Alicata, Parasitolo- 
gist, Hawaii Agricultural Experiment Station, 
for suggesting the original problem and 
making certain facilities of the Department 
of Parasitology available to me; Mr. Paul 
Breese, Director of the Honolulu Zoo, for 
examining and permitting the examination of 
birds in the Honolulu Zoo; Dr. R. W. Hiatt, 
Chairman of the Department of Zoology and 
Entomology, University of Hawaii, for pro- 
viding such excellent facilities for my work; 
Mr. Hiromu Matsumoto, Junior Chemist, 
Hawaii Agricultural Experiment Station, for 
the white rats utilized in this work; Mr. 
Harry Miyata, Miyata Poultry Farm, for per- 
mitting the unrestricted use of his flocks and 
farm; and Dr. M. M. Rosenberg, Associate 
