332 ABSTRACTS OF PAPERS. [VOL. II. 



2. The space which in most species of Acmaea underlies 

 the viscera on the left side in A. tcstudinalis stretches almost 

 across the body, and lacks entirely the ciliated cells character- 

 istic of the nephridium. This negatives the opinion that the 

 space in question is a paired structure whose fellow of the right 

 side is represented by the posterior part of the nephridium. 



3. A sub'raclular organ, whose presence in the Docoglossa 

 has been denied, exists in both A. tcstudijialis and A. fragilis. 

 It is situated on the underside of the odontophore, just behind 

 the tip of the radula, and is a triangular, somewhat cushion- 

 shaped organ, divided by a V-shaped groove into an anterior 

 and a posterior part. The posterior part is marked by trans- 

 verse grooves and is covered by tall, columnar epithelial cells, 

 some of which seem to be ciliated, while others are somewhat 

 fusiform and have much the appearance of sense cells. The 

 innervation has not been traced, but no ganglia are to be found 

 in the organ. The subepidermal portion consists of connective 

 tissue with scattered and inter-crossing muscular fibers. 



IV. THE HABITS AND LIFE HISTORY OF ARGU- 

 LUS WITH REFERENCE TO ITS ECONOMIC 



IMPORTANCE. 



CHARLES B. WILSON. 



IN the town of Warren, Mass., is a small pond which was 

 stocked with carp and bass several years ago. The fish 

 seemed to thrive well until the fall of 1899, when they began 

 to die off in considerable numbers, with no apparent signs of 

 disease or injury. No clue to the cause of the devastation 

 could be obtained till the spring of 1900, when several suckers 

 were speared in the outlet of the pond whose gill chambers 

 were full of the parasitic copepod Argnlus, probably A. cato- 

 stovii. The gentleman who owned the pond stated that these 

 copepods were common on most of the fish caught there, and 

 his statement was afterward verified. On being put in an 

 aquarium with dace, roach, and bream, they attacked these fish 



