30 BULLETIN 817, U. S. DEPT. OF AGRICULTURE. 
The worms have always been apparently underdeveloped, which has 
Jed some to hold the opinion that the sheep ascarids which resemble 
Ascaris lumbricoides are imperfectly grown worms of this species, 
or of Ascaris suum if the pig Ascaris is considered distinct from 
the human Ascaris. In view of the experience of the writers in 
artificially infecting a lamb by feeding the eggs of the pig Ascaris 
it would appear that the common opinion as to the identity of the 
sheep Ascaris is correct. As further evidence of the ability of species 
of Ascaris to undergo at least a partial development in the intes- 
tine of a strange host may be cited the results of our experiment in 
feeding Ascaris suum eggs to a young goat, and it may also be noted 
that Jammes and Martin (1906) record the development of Ascaris 
vitulorum in the human intestine to a length of 8mm. One of these 
writers swallowed A. vitulorum eggs and recovered the young worms 
in- his feces 25 days later. 
LIFE HISTORY OF RELATED NEMATODES. 
The migration of the larve of intestinal parasites through the 
lungs of the host before they finally settle down in the intestine is 
not peculiar to Ascaris. It has been shown by Looss and others that 
the larve of hookworms and of Strongyloides, after entering the 
host through the skin, migrate to the lungs through the heart by way 
of the lymphatics and blood vessels, and then pass up the trachea 
and down the esophagus, finally reaching the intestine. 
The senior writer has observed the larvee of Zemonchus contortus 
(stomach worm of ruminants) in the lung of a guinea pig killed 48 
hours after it had been fed a culture of the larve, which indicates 
that they are able to migrate from the alimentary tract to the lungs 
and perhaps do so normally in their life cycle in their usual hosts, 
sheep, cattle, etc. 
In view of the fact that the larve of forms belonging to diverse 
genera, Ancylostoma, Strongyloides, Ascaris, and, perhaps, Hamon- 
chus, regularly migrate through the lungs before establishing them- 
selves in the intestine, it is quite likely that the phenomenon is one 
of common occurrence in the life cycle of parasitic nematodes. It 
is to be expected, certainly, that forms closely related to Ascaris 
lumbricoides will act similarly with respect to the migration of the 
larvee through the lungs. Stewart (1918a, p. 194) found the larve of 
Belascaris marginata in the liver of mice 1 to 3 days after they had 
been fed eggs of this parasite. The present writers have fed the eggs 
of Belascaris marginata to rats and 5 days later have found the larvee 
in the lungs. The lungs showed petechial hemorrhages similar to 
those observed in the lungs of animals invaded by the larve of 
Ascaris lumbricoides or Ascaris suwm (Experiment No. 8). 
