20 
LIFE HISTORY OF UNCINARIA AMERICANA. 
The life history of the American hookworm has not yet been deter- 
mined in detail, but there is no reason for assuming that it will differ 
radically from that of AgchyJostoma duodenale (see p. 2d.) . , 
In my first description of the worm I stated that the egg in the * 
uterus mav occasionallv contain an embrvo. Since makiup- this obser- 
vation on the females sent to me by Dr. Allen J. Smith I have exam- 
ined hundreds of fresh eggs, but have not found aiw containing ; 
developed embryos. The question ma}^ j 
therefore legitimately arise whether : 
the females originally examined were 
not exposed to the air for some time 
before they were preserved; thus mak- 
ing the development of the eggs pos- . 
sible. If the embryo does develop in 
the uterus, as indicated by some of Dr. ^ 
Allen J. Smith’s material, such an oc- | 
currence is undoubtedly rare. 
DEVELOPMENT OUTSIDE THE BODY. 
Segmentation . — In feces exposed to a 
September, October, or early November 
temperature of the Carolinas, Georgia, 
and Florida, the embrvo develops in 
the egg (fig. 9) in about one day's time. 
In some instances the embrvo develops | 
in less than 21 hours. It is a com- ' 
mon occurrence to find feces 2d hours 
old containing free embryos. j 
The conditions under which the trip was made were not favorable i 
to exact observation in regard to temperature, moisture, etc. It was, 
however, possible to find worms in their first ecdysis about 2 to 3 days i 
after hatching, and worms in the second ecdysis about T to 9 days j 
after hatching. These observations were made under most unfavor- I 
able circumstances, when careful measurements, drawings, etc., were j 
excluded, hence thei^ should be repeated. 
DEVELOPMENT INSIDE THE BODY. 
Experimental infections during the trip were, of course, impossible. 
Fig. 9. — Four eggs of the New World 
hookworm, Uncinaria americana, in 
the 1, 2, and 4 cell stages. The egg 
showing 3 cells is a lateral view of a 
4-cell stage. These eggs are found in 
the feces of patients and give a positive 
diagnosis of infection. Greatly en- 
larged. (After Stiles, 1902b, p. 192, fig. 
127.) 
