THE LEECHES OE MINNESOTA 33 



so that the plates would be slightly thicker than they were finally 

 wanted. As the wax plate congealed, it was cut free from the 

 edges of the pan to prevent its cracking; and when the plates were 

 sufficiently hard, they were lifted out by one edge and laid upon 

 some flat surface until cold, then they were cut into the sizes re- 

 quired. By having several pans of the required size, a large number 

 of plates can be made in a short time and kept on hand ready for use. 

 Two metal strips of the required thickness, as used by Born, 

 were then placed a short distance apart on a piece of plate-glass. 

 Between these strips was laid a sheet of tissue paper, and on this 

 the wax plate of the right size and thickness ; and on top of the wax 

 plate the sheet of paper with the camera-lucida drawing was placed, 

 drawing side up. The surface was then brushed over with a liberal 

 amount of turpentine, and a hot roller, long enough for both ends 

 to rest upon the metal strips was passed over it. The roller which I 

 used was of hollow brass, filled with hot water, which was easily 

 kept at the proper temperature, by means of a Bunsen burner. As 

 the temperature of the roller was always slightly above the melting 

 point of the wax, the superfluous wax was pressed out at the edges 

 leaving the plate of the exact thickness required. The drawings 

 were then cut out, superimposed, and the edges trimmed off in the 

 usual manner. 



PLACOBDELLA PEDICULATA n. sp. 



Habits. 



This leech appears to be a true fish parasite and is found in the 

 gill chamber of the common sheepshead, Aplodinotns grunniens, 

 with the posterior sucker deeply imbedded in the side of the isthmus. 

 In the case of young leeches which have not been long attached, the 

 hole made by the posterior sucker is comparatively shallow, be- 

 ing a mere external depression in the inflamed tissue which sur- 

 rounds it. As the attachment continues the inflamed tissues of the 

 fish grow up like a collar and close in around the leech's body in 

 front of the sucker. This closing up of the inflamed collar presses 

 upon the body of the leech, narrows it to a mere peduncle, and in- 

 cidentally crowds the sucker down into the tissues of the fish so 

 that in time this depression will reach into the underlying mus- 

 cles to a depth of half an inch or more, and have an opening of 

 about a quarter (or less) of an inch in diameter. The bottom of the 



