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THE AMERICAN NATURALIST [Vol. XLII 



fresh-water sheepshead, the posterior sucker of the leech 

 being deeply imbedded in the side of the isthmus or 

 shoulder. In the case of young leeches which have not 

 been long attached, the depression caused by the pos- 

 terior sucker is comparatively shallow, being a mere ex- 

 ternal depression in the inflamed tissues of the fish. As 

 the attachment continues the inflamed tissues of the host 

 grow up like a collar and close in around the leeches 

 body in front of the sucker. This closing in of the in- 

 flamed collar presses upon the body of the leech, narrows 

 it to a slender peduncle in front of the sucker and in- 



cidentally crowds the sucker down into the tissues of the 

 fish, so that, in time, this depression may reach into the 

 underlying muscles 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 depression has a 

 larger diameter. Fig. 1 represents the positions of three 

 depressions from which the leeches have been removed, 

 and one of the depressions cut in two lengthwise. 



These leeches are capable of becoming greatly con- 

 tracted, and when one is disturbed it draws back until it 

 appears as a mere brownish pyriform knob which 

 entirely covers the place of attachment. 



