No. 2.] AATATOA/V OF A SPECIES OF PLATYASPIS. 57 



preserved to enable one, by making total preparations and by 

 serial sectionizing, to recognize all the most important anatom- 

 ical features of the animal, and, in addition, to see histological 

 detail enough to supplement the anatomical identification of 

 the organs. But I have not been able to demonstrate on the 

 preserved material the exact relation of the different members 

 of the reproductive system, or to follow out the branchings of 

 the excretory system. This, and a more careful study of the 

 histology, I hope to make during the coming summer with the 

 aid of living material. In the meantime I will report the facts 

 as already determined. 



I have had only a partial access to the literature of the sub- 

 ject, but gladly acknowledge my especial indebtedness to Monti- 

 celli's article in Leukart's Festschrift, in which he gives some 

 account with illustrations of Platyaspis, and to Stafford's arti- 

 cle on Aspidogaster. These and other articles referred to 

 are indicated at the conclusion of this paper. I am also much 

 indebted to Dr. W. S. Nickerson of the University of Minne- 

 sota, for the privilege of examining his trematode preparations 

 and for friendly advice as to methods of trematode study. 



Habits. 



P. anodoiitae is habitually, if not exclusively, found, not in 

 the pericardial chamber or cavities of the nephridium, but 

 in the mantle chamber, where it is attached either to the sur- 

 face of the visceral mass, the inner surface of the gill, or to 

 the under surface of the kidney, where the mantle and cloacal 

 chambers communicate anteriorly. While I have not made a 

 sufficiently complete search to be able to assert that it is never 

 located inside of the pericardial chamber or kidney, I feel confi- 

 dent that if it is found there that position is not habitual. This 

 point will receive particular attention in my later work. In its 

 location P. anodontae is thus ectoparasitic, and hence decidedly 

 unlike Aspidogaster, which, according to authors, is habitu- 

 ally found inside the pericardial cavity and nephridium. Thus 

 Stafford ('96), p. 8, says : " On opening the Anodonta the 

 parasites are often visible in the transparent pericardium. It 



