Abstract
The nematode parasite Strongyloides simiae of New World monkeys has as a part of its life cycle a free-living phase outside the body of the host. The eggs laid by the parasitic females are passed in the feces, rhabditiform larvae hatched from them feed on bacteria and debris, and under suitable conditions, metamorphose into free-living, sexually mature forms. These adults mate and produce eggs and larvae supposedly identical with those of the first generation. Such second generation individuals have been considered capable only of developing into filariform larvae. Leuckart's 1 views on the fate of the second generation larvae probably have influenced the general belief that only one sexual generation of the free-living phase could develop. The only statement regarding the probable continued propagation of the free-living phase of this organism was that by Faust, 2 who predicted indefinite free-living development.
By planting a known number of S. simiae eggs from the stool of Cebus capucinus imitator which harbored the parasitic females, on a culture medium consisting of a nutrient agar, 2 gm., filtered, aqueous extract of monkey feces, 25 cc., and distilled water, 75 cc., it was possible to observe the entire developmental cycle of larvae and adults and their descendants.
In 4 experiments using the above mentioned medium, free-living sexually mature second generation males were produced on 11 cultures. Five cultures produced second generation females as well. Both sexes of the second generation instead of metamorphosing into filariform larvae retained their rhabditiform characteristics. The males widened posteriorly and spicules appeared. At first no eggs were seen in the young females but with an enlargement of the vulva, eggs appeared in the uterus. In some instances the first generation adults were dead before those of the second generation matured. In most cases, however, the former were present with the latter but soon died while those of the second generation persisted and laid eggs which hatched and developed into third generation filariform larvae.
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