Date of this Version
Journal of Parasitology (September 1917) 4(1): 1-11, + 2 plates.
Also appeared as Contributions from the Zoological Laboratory of the University of Illinois, number 94.
For many years I have been engaged in the study of parasitic worms from North American freshwater hosts, mostly fish; during this time I have had opportunity to examine and compare material from a large number of localities embracing many widely separated points. In this work I have been aided very greatly by studies on individual groups undertaken and published under my direction by various graduate students to whom my obligation is freely expressed here. In connection with this work it has been necessary to examine critically all original records of parasites from similar hosts and to endeavor to reach a positive determination of the parasite under discussion in each case. This is not a simple matter, as the records were often made on the basis of a rapid preliminary examination; furthermore, the total lack of special reference works on these groups led to the recording of parasitic species under general names taken from the older European writers, and these names are of ten wanting in definite significance.
My work has naturally led to the discovery of new facts regarding the structure of the forms studied and has compelled me to introduce new names and to rearrange forms so as to express better their correct relationships in the light of more perfect knowledge of their structure. Such changes are of course unfortunate in that they make it difficult to trace the continuity between the new and the old in zoological literature; they are nonetheless essential if the student is to apprehend the true character and affiliations of the forms with which he comes in contact. It has been my fixed principle never to make any changes until I was personally familiar with the form discussed or had acquired such acquaintance with its structure as to know that some change was inevitable and that the proposed modification was defensible on morphological grounds. Most of the questions involved in the changes listed later in this paper have been submitted to the criticism of advanced workers in the field, or discussed before graduate classes for some years so that they may be regarded as seasoned changes.
Some of the more general results of my work have been included in brief form in synopses of the Parasitic Flatworms and Parasitic Roundworms which constitute two chapters in Freshwater Biology by Ward and Whipple just being published by John Wiley and Sons, New York. It seems to me wise to print here in outline the most important new material regarding the structure and classification of the parasitic forms discussed in these chapters as there are items which might easily escape notice and thus lead to confusion if published only in a textbook. The work just cited gives complete summaries of the North American forms in the groups mentioned and the place of the items discussed later in this paper may be precisely determined by reference to it. These items are arranged here in the order in which they are taken up in the book, and this is the systematic arrangement. The student will also find there an abundance of illustrations to demonstrate the points discussed here.
Taxonomic Changes among Trematoda
Larval Stages of Trematoda
Morphology of Nematoda