On Specificity of Opalina in the Frog.

Abstract

It is well known that the ciliate, Opalina, parasitic in the rectum of the leopard frog, Rana pipiens, and in the pickerel frog, R. palustris, occurs but rarely or not at all in the closely allied adult green frog, R. clamitans, and bull frog, R. catesbiana. Tadpoles of R. clamitans have been found by us to be almost universally parasitized. 1 Experiments by the first author were conducted to determine if Opalina would live and reproduce when transferred directly from the rectum of R. pipiens to that of the two genera of green frogs.

The frogs used in these experiments included R. pipiens, R. clamitans, and R. palustris, collected within 70 miles of New Brunswick, N. J., and R. catesbiana from New Orleans, La. The parasite employed in these transfers was O. obtrigonoidea. Removal of the rectal contents was accomplished with the aid of a fine glass pipette introduced through the cloaca of the host after previously relaxing the surrounding muscles by the action of M/8 magnesium chloride for 20 minutes. A pipette full of Ringers solution was first forced into the rectum before withdrawing the contents for examination or for introduction into a second host. The experiments were carried on from October to late May of the following year. The green frogs and bull frogs used in these experiments were examined in each instance prior to inoculation. One specimen of clamitans was found to harbor a heavy infection of Opalina, due, possibly, to contamination from close proximity to pipiens and their faeces, since the former frog does not normally harbor these parasites.