10 BULLETIN 817, U. S. DEPT. OF AGRICULTURE. 
Although we are ignorant of the determining cause of hatching, 
nevertheless we can reach certain conclusions as to the place and 
manner in which hatching occurs, as follows: When Ascaris eggs 
containing fully developed embryos are swallowed they do not regu- 
larly hatch in the stomach, but pass to the small intestine, where they 
begin to hatch within a few hours after the eggs are swallowed. The 
eggshell is not dissolved by the digestive juices, the embryo being re- 
leased by a split in the shell through which it emerges by its own 
efforts. Ascaris eggs may hatch not only in animals in which the 
parasites can develop to maturity, but apparently in almost any mam- 
mal that swallows the eggs, provided the embryos within the eggs 
have reached a stage in which they are ready to hatch. 
LARVAL STAGES OF ASCARIS. 
MIGRATIONS OF LARVZ IN BODY OF THE HOST. 
It has been stated that in artificially infected rats, mice, and other 
animals newly hatched Ascaris larve may be recovered in the feces 
within a few hours after the eggs have been swallowed. Stewart 
(1916-1918), however, discovered that not all the larve were thus 
eliminated, but that some migrated out of the alimentary tract into 
other parts of the body and soon appeared in the liver. Stewart 
(1916a) found larvee in the liver of a mouse (in dilated blood capil- 
laries) which died four days after being fed eggs of A. lumbricoides. 
In this animal the larve had also reached the lungs (in the air vesi- 
cles). He found larve of Ascaris marginata in the liver of mice 
within 24 hours after administration of the eggs, none having yet 
appeared in the lungs (Stewart, 1918a, p. 194). Our experiments 
show that the larve after leaving the lumen of the intestine soon 
appear in the liver, and may be found there before they are evident 
in the lungs. For example, a mouse killed 51 hours after feeding 
with Ascaris suwm eggs showed numerous larve in the liver, but 
none could be found in the lungs or spleen. Frequently as late as 
five days after feeding Ascaris eggs to mice we found larve only in 
the liver, none having yet reached the lungs. In one instance, eight 
days after it had been fed Ascaris suum eggs, a mouse was killed and 
larve were found only in the liver. 
The newly hatched larve of Ascaris suwm measure about 0.2 
to 0.8 mm. in length. In the liver the larve may grow to a length 
of 0.86 mm. (mouse nine days after infection, lungs and various 
other organs also infested), reaching a stage of development similar 
to that of larve of corresponding size in the lungs. 
Ascaris larve commonly disappear from or at least become scarce 
im the liver within from 4 to 10 days after infection, but we have 
found numerous larve in the liver of a mouse as late as 23 days after 
