UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 817 
Contribution from the Bureau of Animal Industry 
JOHN R. MOHLER, Chief 
Washington, D. C. PROFESSIONAL PAPER May 12, 1920 
OBSERVATIONS ON THE LIFE HISTORY OF 
ASCARIS LUMBRICOIDES. 
By B. H. Ransom, Chief, and W. D. Foster, Junior Zoologist, Zoologival 
Division. 
CONTENTS. 
Page. Page. 
Historical summary 23223 is chee eb! 1 | Larval stages of Ascaris—Continued. 
Probable identity of Ascaris Humbri- Relation of host to size of de- 
coides and Ascaris suwm_______ 4 V.CLOPIN Ge NaN ee ae ae 19 
Ege stage of Ascaris__2___=--__- 4 Lesions associated with migrat- 
ANCubATION Ss <eieod Wh eater 4 ing glare = ieee 21 
Incubating Ascaris eggs for ex- Death of migrating larve_____ 23 
perimental use ==) 2 ee 5 | Relation of age to Ascaris infes- 
Longevity of Ascaris eggs_____ 6 VEIN OE SS oe ee Se Lee 24 
Resistance of Ascaris eggs to AUSCUPUS a) paren iin pi ei yee ee Se 27 
chemical” agents. 2 Gs 6 Longevity of larve outside the 
Avenue of infection with As- NOSE = ee Sete 29 
CUTTS eae a EOI a EY qT Natural occurrence of Ascaris in 
Hatching of Ascaris eggs______ 8 Slice pres ee ae 29 
Larval stages of Ascaris__________ 10 | Life history of related nematodes__. 30 
Migrations of larve in body of Details of experiments! with Ascaris -. 31 
TORS OS tae eee er ee ee foe GeneralsumMmMany 223k eee 43 
Development in the intestine. _ 15) | Bibliography -——2-—= === 222-2 45 
Description of larval stages___ 18 
HISTORICAL SUMMARY. 
The results of experiments by Lutz (1888), Epstein (1892), and 
other investigators, together with various considerations of general 
and special nature, have led to the acceptance of the belief to the 
extent that it has been taken as an established fact that Ascaris /wm- 
bricoides and Ascaris suwm, parasites of man and the pig, respec- 
tively, have a direct hfe history and require no intermediate hosts in 
their cycle of development. Recent work by Stewart (1916-1918), 
however, has shown that the life history of Ascaris is not so simple 
as commonly SUOSSBE and is has made the sue inter or one and 
1This paper was written teat the death of Mr. Foster, a one occurred Onna 6, 
1918, but in view of his participation in the investigations upon which the paper is based 
his name appears as joint author. 
137550°—20—Bull. 817——2 
