38              Incidence of Strongyloides papillosus Wedl, 1856

the life-history of the genus. The latter has been developed for the con-
servation of the species under conditions commonly obtaining in less favour-
able milieu, as, for example, human strains in cooler climates. At the pre-
sent time there is no evidence of a genetic distinction between indirect and
direct modes of development in species of Strongyloides on which adequate
clinical and experimental studies have been conducted ".

Wedl [1856] discovered and named the common ovine species (S. papil-
losus) ; Pagenstecher [1865] described a Strongyloides from pigs before
Bavay [1876] described the human species of Strongyloides (S. stercoralis).
Species of the genus Strongyloides have since been described from many groups
of vertebrates—birds and several species of herbivorous, carnivorous and
omnivorous mammals. In India, Ware [1923] appears to be the only worker
who has recorded a Strongyloides infection in a fatal case of Strongyloides
stercoralis in a dog.

The record of Strongyloides papillosus is the first for this Province and
possibly for India.

                                  CULTURE STUDIES

In faecal cultures at 27° to 30° C.—range of the laboratory room tem-
perature at Madras during the studies—the eggs passed by the parasitic females
hatched within a very few hours and gave rise to rhabditiform larvae (Fig. 8).
They grew rapidly. At first, a small portion of them turned into filariform
(infective) larvae from about forty-eight hours after culture; the large re-
mainder developed sexual characters entering into the rhabditiform, free-
living generation. The females were very numerous but the males were
consistently missed. Zilahy [1936] states, the males are very rarely seen.
It has been suggested that the males make their appearance long before the
females and disappear by the time the females preponderate. Probably they
mate during the first few days of life as mature individuals before the ferti-
lized females passed eggs and these in turn gave rise to the second generation
of filariform larvae. They were usually found in cultures after four or five
days. In these culture conditions, a second generation of free-living
forms developing from the eggs passed by the free-living female, could not be
detected. Rogers [1939 ] during his studies on Strongyloides cati, under culture
conditions, has seen a few second generation males similar to those of the
first.

                  THE FILARIFORM (INFECTIVE) LARVA

                                    (Figures 4, 5 and 10)

The infective larvae developed directly from the first rhabditiform stage
hatching out of the egg laid by the parasitic female or indirectly from the
rhabditiform larvae arising from the free-living females. The two types of
infective larvae developing from these were indistinguishable. The change
from the rhabditiform into the filariform character occurs while the larva is
still in the lethargic condition. Soon after awakening it releases itself from its