A morphological distinction between infective larvae of Ancylostoma and Necator.

Abstract

Infective larvæ of Necator americanus, Ancylostoma duodenale and Ancylostoma caninum, in which the stored food granules were reduced till the internal organs were clearly visible, were studied for morphological distinctions. The reduction of the food granules was obtained either by keeping the larvæ in soil cultures for 5 weeks and more, or by aging them artificially through increased activity. The latter method was devised by F. K. Payne (1923) and consists in burying the larvæ at the bottom of a jar filled with moist sand. The larva will migrate in great numbers up to the surface and during this time of activity rapidly use up their stored granules.

In these attenuated larvæ a difference at the point of union between the oesophagus and intestine was found to exist between larvæ of N. americanus on the one hand and those of A. duodenale and A. caninum on the other hand, indicating the probability of this being a generic distinction.

When Necator larvæ are studied under a 16 mm. objective, it appears as if the oesophagus and intestine were separated by an open space distally marked off by a definite transverse line, while in Ancylostoma larvæ the intestine is seen to follow as a direct continuation of the oesophagus. Careful study with an oil immersion objective reveals the fact that the lumen of the oesophagus is connected with the lumen of the intestine through a fine canal surrounded by a thickened part of the wall. This apparently functions as a sphincter. In Ancylostoma larvz the inner outline of this sphincter follows as a continuous curve into the inner outline of the intestinal wall. Necatar larvz have the distal part of the sphincter protruding into the lumen of the intestine in the form of a papilla separated from the intestinal wall by a groove. In high and in low focus the proximal arch of this groove appears as a transverse line at the base of the papilla. It is this line which stands out so strikingly under low magnification when the whole thickness of the larva is near focus at the same time and the optical impression of the part of the arch behind as well as the part in front of the papilla reaches the eye of the observer simultaneously.