Experimental Studies on Eggs and Miracidia of Renifer aniarum (Leidy,1891) and Dasymetra villicaeca (Byrd,1935)

Abstract

Previous investigators of trematodes of the Subfamily Reniferinæ, to which the 2 species studied by the writer belong, have found the eggs fully developed when oviposited. In the present studies 2 groups of parasite-free Physa halei Lea (the snail host) were inoculated October 1 and October 6, 1936, respectively with freshly oviposited eggs of Renifer aniarum (Leidy, 1891), which no doubt had been naturally incubated in the uteri of the trematodes while in the mouth of the snake, Natrix cyclopion (Duméril and Bibron), and shed cercarial larvae of this fluke 36 days later. During the 30 days previous to the dates of inoculation the mean air temperature was 28°C. in the laboratory where the snakes were kept. Subsequently 3 groups of parasite-free P. halei were inoculated with eggs of R. aniarum November 4, 11, and 20, 1936, respectively, and one group of parasite-free P. halei was inoculated November 20, 1936, with eggs of Dasymetra villicaeca Byrd, 1935. Individuals from these 4 groups were later fixed at various time intervals after the dates of inoculation and were found on careful examination to be uninfected. Daily attempts were then made to hatch freshly oviposited eggs in the digestive tract of the appropriate snail host, with negative results, During October, 1936, the mean air temperature was 22.5°C. and during November, 1936, 15.7°C.

The eggs of both species, embryonated 1–30 days at room temperature (17–20° C.) failed to mature. Experiments demonstrated that during the colder months it was necessary to incubate artificially the freshly oviposited eggs for a period of 6 days at a temperature of 25° to 30°C. to produce mature and usually viable eggs so that, after the ingestion of these eggs by the appropriate snail host, hatching would occur. Artificial incubation of eggs of both species was unnecessary after April 15, 1937.