THE LEECHES OE MINNESOTA 93 



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

 muscles of the host to a depth of half an inch or more and have an 

 opening of about a quarter of an inch or less in diameter. The bot- 

 tom of the depression has a larger diameter. Figure 5 of plate C repre- 

 sents the positions of three depressions from which the leeches have 

 been removed, and figure 6 represents one of the depressions cut in 

 two lengthwise. 



These leeches are capable of becoming greatly contracted and 

 when one is disturbed it draws back until it appears as a mere 

 brownish pyriform knob which entirely covers the place of attach- 

 ment. 



The burying of tlie posterior segments in the tissues of the 

 host has brought about an interesting structural change, so that 

 we find the anal opening- shifted forward to a position between 

 somites XXIII and XXIV instead of between somites XXVII and 

 XXVIII as in the other members of the genus. It is noticeable 

 that, while the young leeches whose posterior portions are not yet 

 deeply imbedded have the characteristic position of the anus 

 (XXIII/XXIV), the outline of the posterior part of the body is 

 still a regular curve showing none of the pedicular characteristics 

 so pronounced in the older individuals. The posterior sucker, how- 

 ever, is very strongly developed even in those not more than a 

 centimeter long. 



Practically nothing is known of this leech separate from its 

 host, but it seems possible that a part of its existence may be spent 

 elsewhere. During September, 1903, I examined several thousand 

 specimens of the sheepshead from Lake Pepin and found only three 

 isolated leeches, each about a centimeter in length. The posterior 

 sucker, while imbedded in the tissue, was not sunk in deeply and 

 so had not produced the characteristic peduncel. They were evi- 

 dently young ones which had recently attached themselves to their 

 hosts and were gradually sinking the posterior sucker into the 

 host's flesh. As full grown specimens, deeply imbedded, were 

 found in the same locality during August of 1899, at least ..some of 

 the adults must remain with their hosts during the summer and 

 probably thruout the year. 



