10 TWELFTH ANNUAL REPORT. 



all found affected, some having as many as five parasites of various 

 sizes about the alimentary canal, in the common vascular cavity 

 which corresponds to the entire arterial and venous system of the 

 more highly organized Calanidas. The Cercerian or tailed stage 

 was not found. Were the life-history known it would probably 

 appear that the larval stage is passed within some young moUusks, 

 and that the adult infests some vertebrate, probably fish, and 

 would thus be perhaps transferred either in food or drink to 

 the human system. 



It is worthy of notice that the host was soon destroyed by the 

 parasite, the post-imago or coronatus form being absent ; most 

 of the individuals thus infested possessed abnormally persistent 

 larval characters in antennae, etc." (See also below on Lagenella 

 mobilis). 



The external parasites are more numerous but, in the main, less 

 dangerous. Among these are a variety of algse, and colonies of Vor- 

 ticellse and related animals. There is almost always a colony of 

 Acineta near the anus of Cyclops phaleratus. Rarely Stentor is 

 found upon the body of Cyclops. 



The most remarkable ectoparasite among the protozoa is the 

 remarkable louse-like ciliate protozoan, to be described beyond, 

 found as a parasite of Diaptomus pallidus. 



Finally, certain of the rotifera are very constant enemies of the 

 entomostraca, one species making its diet almost exclusively of 

 Chydorus spheericus and stowing them away with remarkable 

 facility with its forceps-like jaws. 



A New Species of Corethra. 

 (Plate V. Figs. 1-4 ) 



The Corethra plumicornis as knq^n in the larval form is one 

 of the most abundant of the inhabitants of our inland waters, and 

 its form and habits are sufficiently well known. (See Types of 

 Animal Life by the author for description and figures.) 



A second, and presumably new, species was found in a night 

 gathering from Lake of the Isles near Minneapolis. In motion it 

 differed so entirely, though indescribably, that the eye recognized 

 it at once as new. The few specimens then obtained were all that 

 have been seen, but I will here give a brief description of the larva 

 and pupa in hope that the imago may finally be encountered. 



