4 BULLETIN 817, U. S. DEPT. OF AGRICULTURE. 
PROBABLE IDENTITY OF ASCARIS LUMBRICOIDES AND ASCARIS 
SUUM. 
The common intestinal roundworm of man (Ascaris lumbricoides) 
and the corresponding parasite of the pig (A. suwm Goeze or A. 
suilla Dujardin) are morphologically indistinguishable and prob- 
ably are specifically identical. Whether or not infection of man from 
worms harbored by the pig, and vice versa, commonly occurs is un- 
known and it has not yet been shown by experiment whether or not 
the offspring from worms harbored by one host can reach fertile 
maturity in the other. Although there is no good reason for con- 
sidering the two forms to be distinct, in the present paper the pig 
Ascaris will be referred to as A. suwm and the human Ascaris as 
A. lumbricoides, so that it may be clear in any given case whether 
the parasite came from a pig or from a human host. : 
EGG STAGE OF ASCARIS. 
INCUBATION. 
When deposited by the adult female in the intestine of the host 
animal the egg of Ascaris is in an early stage of segmentation. 
Segmentation progresses during the passage of the egg through the 
intestine. If the egg is not promptly eliminated in the feces of the 
host, however, segmentation does not continue and development of the 
embryo comes to a standstill. Martin (1913) found by experiments 
in vitro that at the body temperature of the host segmentation pro- 
gresses rapidly up to a certain limit, but development of the embryo 
is completed only at lower temperatures. Because of the inhibiting 
effect of the body temperature it is necessary for the eggs to pass 
out of the intestine of the host before they can develop to the infec- 
tive stage. Outside the body the development of the eggs is chiefly 
influenced by three factors—temperature, moisture, and oxygen 
supply. At low temperatures development. proceeds slowly .and 
may stop entirely if the temperature is low enough, so that the time 
required for the embryo to develop to the final stage reached in the 
ego may vary from a few days to many months and possibly several 
years. 
Martin (1913) found the optimum temperature for the develop- 
ment of the eggs of Ascaris vitulorum (of the ox) and A. suwm to be 
about 33° C. We have noted that a considerable proportion of the 
egos of A. swum kept at this temperature contain fully developed 
embryos at the end of 10 days, and practically all complete their de- 
velopment within a month. In the absence of moisture, development 
is inhibited and extreme dryness may ultimately destroy the vitality 
of the eggs. The moisture requirements, however, are slight. . Ross 
(1916) found that eggs of A. Jumbricoides placed on glass slides and 
