i8 Roosezfelt Wild Life BuUcfm 



large part of the middle area of the thirteenth and fourteenth 

 segments. They open exteriorly on the ventral surface by four 

 pores arranged at the angles of a nearly perfect square, two of them 

 in the furrow between segments thirteen and fourteen and two in the 

 furrow between the first and second rings of the latter segment. Sur- 

 rounding each of the pores is a slightly swollen region extending 

 over the contiguous halves of the tv\^o rings betvN^een which the pore 

 lies. A\'hen fully developed in sexually active leeches the four 

 swellings together form a conspicuous rough quadrate area extend- 

 ing over three rings and diAided into quarters by narrow longitudinal 

 and transverse diametral furrows. 



The surface of the body is quite smooth and free from papillae 

 although in some preser\-ed specimens it may be somewhat roughened 

 by the projection of the scattered sense-organs. This refers espec- 

 ially to the organs of touch or mechanical sense which are distributed 

 over the surface of the skin generally but are especially numerous 

 on the lips. Other sense-organs are those of taste, or chemical 

 sense, located on the lips; the eyes, already referred to, which are 

 strongly sensitive to changes in the intensitv^ of light ; and the 

 sensillae, of which a circle occurs regularly on the middle ring of 

 each segment and which are weakly sensitive to the same stimuli. 

 The latter appear as minute clear white spots of which those on the 

 dorsal surface stand out ver\- conspicuously on the dark green back- 

 ground. 



The external openings of the nephridia or kidney tubes appear as a 

 pair on the under surface of the second ring of each of the fully 

 developed or five-ringed segments of the middle region of the body. 

 These are not, as formerly supposed, organs of respiration. It has 

 been obsen'ed when the leech is drawing blood in the open air, as in 

 blood-letting, that drops of clear fluid appear at these openings and 

 flow over the surface of the body. This is believed to be derived from 

 the blood-serum wiiich is drawn off. thus greatly increasing the ani- 

 mal's capacity for the solid parts of the blood and at the same time 

 serving to keep the skin moist. The anus is a small dorsal opening in 

 segment twentA'-seven immediately above the posterior or caudal 

 sucker, which is a large and circular disk attached by a broad pedicle. 



The mouth is of large size and may be considered as coextensive 

 with the entire opening of the oral sucker, the upper lip of which 

 overhangs it. The jaws have the usual triradiate arrangement, but 

 among the leeches of the United States, the form is characteristic. 

 They are compressed and about tAvice as long as high, and each bears 

 along its ridge a single row of about sixt3--five fine, conical, slightly 

 retrorse teeth with bilobed bases. A verv- short muscular phar\-nx, 

 with the lining thrown into several longitudinal folds, reaches to about 

 the ninth segment, within which is a still shorter oesophagus scarcely 

 to be distinguished from the croplike stomach, inasmuch as the 

 sacculations begin immediately. From the tenth to the eighteenth 

 inclusive each segment includes tv\-o pairs of lateral gastric caeca, of 

 which those from the thirteenth baclcn^ard are of large size and 

 branched. The last pair, which originate from the stomach in the 



