Larval Stages in a Protozoon

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Abstract
The name Opalina larvarum Metcalf given provisionally to a species in tadpoles of Rana clamitans is definitively confirmed. This Opalina infects the tadpoles only, not passing through the metamorphosis into adult frogs. After conjugation its zygote passes through several larval stages living for some weeks and reproducing asexually in each stage, being successively a Protoopalina, a Cepedea, a broad Opalina, and finally a narrow Opalina, thus confirming conclusions as to the evolution of the Opalinidae previously drawn on anatomical grounds. Tadpoles (not adults) of Rana catesbeiana carry an as yet unnamed Opalina, the sequence of whose larval stages is Protoopalina, Zelleriella, Opalina of the broad subgenus, and finally Opalina of the narrow subgenus. Reference is made to the evolution of the Opalinidae as a shuffling of 4 separately inherited trends.

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