40 HIRUDO. 



It seems to me that sufficient distinctions are afforded among leeches 

 to constitute species, by very definite characteristics among the whole 

 twelve enumerated. Yet authors have not been so fortunate as to seize 

 those, and placing individuals beyond all doubt and difficulty. 



The figure of the Chequered Leech, at rest, is the longitudinal half 

 of a pear, between five and six lines in length, by about the same in 

 width across the longest diameter ; when extended, it stretches about 

 two inches and a quarter, when the width at the base is three lines, and 

 the diameter of the sucker one line. The anterior extremity when ex- 

 tended, is somewhat of a long lanceolate form, with four pair of black 

 eyes down the middle, very distinct, the outer pair rather smaller than 

 the others. The body is environed by a broad, thin, crenate, not chequer- 

 ed margin, with a row of yellow tubercles. 



The body is divided into segments somewhat broad, and divided by 

 narrow circles. Its substance is wholly gelatinous quivering with the 

 slightest motion. 



This is infinitely the finest and most beautiful of the Scotish leeches, 

 generally of a fine translucent green, speckled black and yellow. Some- 

 times there appear several longitudinal rows of yellow specks interspersed 

 with black specks ; sometimes all are disposed with less regularity. 

 Plate IV. fig. 24. Hirudo tessellata, quiescent, under surface ; 25, in motion, 

 upper surface ; 26, eyes ; 27, margin ; all those figures somewhat en- 

 larged. 



The colour undergoes considerable variation. It fades as the water 

 becomes stale, and revives in a deeper green when renewed. The belly 

 is leaden-grey, minutely speckled. 



The viscera of this leech are more numerous, and of different forma- 

 tion, from those of any others. When replete they are alike conspicuous. 

 and probably less so, according as they are more or less empty. They seem 

 constructed after the same general plan, however, as the viscera of the com- 

 planata and stagnalis. In a small specimen replete with food, they seem- 

 ed to consist of eighteen pair diverging from right and left of the main 

 trunk or stomach. Fig. 28, back ; 29, belly ; 30, the same enlarged. 



I have been unable to ascertain the nature of the food, which may 



