Observations and Experiments on the Opalinid Ciliates of the Green Frog

Abstract

This is a continuation of studies begun a number of years ago (Hegner, 1922) because of the fact that the tadpole of green frogs and bull frogs have a high incidence of infection with opalinids, whereas the adults are usually free from these ciliates, although both tadpoles and adults of other American frogs are infected. The chief questions involved are (1) when and why do green frog tadpoles lose their opalinids and (2) why do not adult green frogs become reinfected? Green frogs, leopard frogs and tree frogs from Mount Desert Island, Maine, were studied during the summer of 1930 in an attempt to answer these questions. Do adult green frogs on Mount Desert Island, Maine, harbor opalinids? This was the first problem undertaken. Ten adult green frogs of various sizes, and presumably of various ages, were examined. No opalinids were found. Ciliates of the genus Nyctotherus were present in the rectum of one specimen; trichomonads were present in large numbers in all; hexamitas were found in nine, but were few in number. At what stage does the green frog lose its opalinids? To answer this question tadpoles were separated into three groups as follows: (1) without external legs, (2) with two posterior legs, and (3) with four legs. The lengths of body, tail and intestine were obtained for those with two and four legs and presented in the following table.