18 BULLETIN 817, U. S. DEPT. OF AGRICULTURE. 
tarded by the fact that they were in an abnormal ‘host. We have 
observed full-grown Ascaris in a pig 11 weeks old, so that it is evi- 
dent that the parasites may attain maturity in pigs within 24 months 
after infection. We may therefore conclude that Ascaris, both in 
human beings and in pigs, may reach maturity 
as early as 24 months after infection. 
DESCRIPTION OF LARVAL STAGES. 
The newly hatched larve vary somewhat. in 
size, commonly between 0.2 and 0.3 mm. in length. 
es nscale oun The specimen figured (figure 2) measured 0.22 
Yee containing fully mm. in length, 0.013 mm. in maximum thickness, 
A ecned See esophagus 0.09 mm. in length, distance of excre- 
tory pore from anterior end of body 0.05 mm., 
and distance of anus from the tip of the tail 0.04 mm. The diameter 
of the body is nearly uniform throughout, head rounded, tail conical. 
On the anterior aspect of the head is a small, rounded knob, the so- 
called “tooth” of the Ascaris larva. This knob, according to Stiles 
(1891), is composed of three parts, corresponding to the lips of the 
adult Ascaris. In living specimens the outlines of the esophagus 
except posteriorly can not ordinarily be distinguished and the nerve 
ring is not apparent. This portion of the body is very clear, and 
free from color or conspicuous granules. The intestinal cells contain 
numerous small, yellowish- brown granules. The genital 
primordium is not evident in lving specimens. 
Before hatching, the larva (figure 1) is inclosed in a 
close-fitting, delicate cuticular sheath (shown in figure 2). 
When the larve are artificially expelled from the eggs (by 
applying pressure) they retain the sheath or in some cases {| 
cast it off as they emerge from the eggshell. Atthe anterior [-}* 
end the sheath is supplied with a crown of oe 
minute papille, apparently 6 in number. 
Under normal conditions it may be presumed 
that the larva undergoes its first molt at the 
time of hatching or shortly afterwards, fol- 
lowing which at least another molt appar- 
ently occurs before the larva reaches the stage 
at’ which it migrates from the lungs to the 
Fic. 2—Asecaris suum. 
intestine. Newly hatched larya in- 
The larve in the lungs reach a length of PRSGUN EN GUA ULEE Sc 
Magnified 375 times. 
5 to 10 times that of the newly hatched larve. 
The specimen shown (figure 3) is from the lungs of a rabbit 10 days 
after infection. It measures in length 1.43 mm., in maximum thick- 
ness 0.065 mm., length of esophagus 0.23 mm., distance of nerve ring 
from anterior end of body 0.11 mm., distance of excretory pore from 
