

THE LEECHES OF MINNESOTA 95 



VIII and by somite X present the following typical arrangement: 

 The neural annulus bears a median one and a pair just mediad of 

 the dorso-lateral sensillse. A3 bears a pair directly in line with the 

 dorso-median sensillse and ai a smaller median one. 



This species exhibits the same gradual development of the bian- 

 nulate and triannulate somite as P. parasitica and consequently pre- 

 sents the same difficulties in the application of a formal descriptive 

 terminology. Somites I and II may be considered as uniannulate, III, 

 IV and V as biannulate, VI as transitional and VII to XXIV or XXV 

 as triannulate ; XXVI and XXVII exhibit partial subdivision only at 

 the margins. The complete somites of the middle region of the body 

 show the same tendency of the sub-division of a J and aj into secondary 

 annuli that is exhibited by P. rugosa. In the internal anatomy a con- 

 siderable number of minute differences between this species and 

 P. parasitica have been observed, but the general and obvious structure 

 of the alimentary canal and reproductive organs of the two species is 

 essentially alike. 



The colors as described from living eastern representatives of 

 the species are rather characteristic. The dorsum is generally a light 

 olive green varigated with brown, pale yellow, and colorless areas. 

 The head end lacks pigment almost entirely except what is concen- 

 trated about the eyes and in the transverse bands on the neural annuli. 

 This light area extends caudad for some distance as a median vitta 

 between the pairs of small eyes. On the neural annuli it is usually 

 interrupted by the transverse bands of interocular pigment between 

 which it is flanked by dark cloudings which more posteriorly takes 

 the form of a pair of dark longitudinal bands just mediad of the dorso- 

 median sensillae. At about somite X and thence caudad, the median 

 vitta and its dark flanking bands are transformed into a chain-like 

 pattern consisting of alternate dark bars and elliptical rings with light 

 centers, the former extending over about two somites and the latter 

 one somite, there being about five of each. Posteriorly an elongated 

 light median area represents several of the rings coallesced. 



The larger cutaneous papillae are of a light yellow or cream color 

 and those of the most medial neural series interrupt the dark bands 

 described above. A similar yellow color occurs along the margins, 

 alternating in blocks with the green ground color. In many speci- 

 mens narrow bands of dark pigment extend across the entire dorsum 

 of the anterior neural annuli and less frequently all or nearly all of 

 the sensillae are flanked on the medial side by brown or black pig- 

 ment. The ventral surface is nearly plain. 



