Homologies of the Excretory System of the Forked-Tailed Cercariae: A Preliminary Report

Abstract

Very little is known of the homologies of the protonephridial system in the various subdivisions of the Trematoda.Most of the anatomical studies on this group have been made from toto mounts and serial sections of preserved material, in which locating the flame cells and tracing the finer branches of the excretory system is practically impossible.My work has convinced me that a more complete knowledge of this system will do much to clear up relationships and to establish natural families.Also an increased knowledge of the excretory systems of little known types of cercariae will be of great help in solving life-histories by suggesting the groups of adults to which such forms belong.In certain cases the close relationship of two cercariae may be shown by comparisons of their excretory systems; when on account of differing degrees of development of adaptive gehen characters they superficially appear to be very different.The work on larval trematodes of which this paper forms the first published part was carried on at the University of Michigan Biological Station at Douglas Lake, Michigan, during the summers of 1914, 1915, and 1916.The region around Douglas Lake is very favorable for work on these forms since an abundance of material of a large variety of trematodes is readily available.I wish to express my appreciation to the University of Michigan Biological Station for facilities provided for carrying on this work.Thanks are due Mr. H.B. Baker for the identification of the molluscan hosts.The best results in tracing the excretory systems of larval trematodes can be obtained.from high power studies on living animals.To make such work effective it is important to have an abundance of material.By using thin cover glasses and slowly removing the water from the preparation even cercariae so small that they are almost invisible to