The Life History of Gongylonema scutatum

Abstract

In April, 1911, the writers undertook some investigations in regard to insects as intermediate hosts of parasites. The investigations of the sefior author were carried on at the Experiment Station of the Bureau of Animal Industry at Bethesda, Md., and in the laboratories of the Bureau at Washington, and later at Colorado Springs, Colo. Those of the junior author were carried on at Colorado Springs, Colo. Particular attention was paid to the dung beetles, as it seemed evident that these insects in working through fresh feces as is their habit, would have the first opportunity to ingest eggs of worms parasitic in the digestive tract of cattle, sheep, and other live stock. Such beetles as species of Aphodius, furthermore, appeared small enough to be readily ingested by grazing animals, and the beetles' habit of flight from one manure deposit to another offered chances for such ingestion, as the beetles' flight commonly terminates on grass and herbage with which they might readily be swallowed by cattle or sheep. The dissections by the senior author of Aphodius femoralis, A. granarius, A. fimetarius and Onthophagus hecate resulted in the finding of encysted larval nematodes in the body cavity. These cysts were about 0.5 mm. in diameter and as many as 8 were found in one Aphodius and 15 in one Onthophagus hecate. One larva which was measured was 2 mm. in length and 50t in thickness. Viewed from in front the head shows a narrow mouth aperture elongated dorsoventrally and surrounded by a chitinous border, which is oblong quadrangular in outline with rounded corners, and measures about 12Ft dorso-ventrally and about 8, from side to side. A short distance posterior of the edge of the chitinous border are 2 sub-dorsal and 2 subventral papillae. The chitinous border of the mouth is raised above the surrounding surface of the head and resembles a projecting flange when the head is viewed from the side. The slender pharynx is 40,u long. The esophagus measures about 1.5 mm. in length, and is differentiated into a slender anterior portion about 225t~ long, and a more granular posterior portion of somewhat larger diameter. The anus is about 1001 from the tip of the tail. The latter is blunt and is supplied with two or three very small short conical processes. The excretory