42 bulletin: museum of compakative zoology. 



stagnalis more closely than those of any other species (compare Figures 1 

 and 27). 



The crop (I'glv., Figure 27), as in G. stagnalis, bears a single pair of diver- 

 ticula, which arise in the middle of somite xix. ; but the diverticula are 

 shorter in this species than in stagnalis, ending usually in somite xx. (com- 

 pare Figures 1 and 27). The stomach (^ya.), as in all species of Glossiphonia, 

 bears four pairs of lateral diverticula. They arise within the three somites 

 xx.-xxii. All are directed slightly forward. The intestine (in.) is a simple 

 tube not constricted into distinct chambers proximally as in most species. 

 The anus (an., Figure 24) lies just behind somite xxvii. 



In the structure of its digestive tract, as well as in the composition of its 

 somites, this species shows a more reduced, simpler condition than is found 

 in any other species known to me, stagnalis coming nearest to it in these 

 jjarticulars. 



e. Nervous System. 



On account of the transparency of the body the central nervous system can 

 be studied with ease in this species, either in the living animal or in whole 

 preparations. In the ventral ganglionic chain there are, as in all species of 

 Glossiphonia, twenty-one distinct ganglia. These innervate somites vii.-xxvii. 

 respectively. 



The brain (cb., Figures 23, 27; also Figures 25, 26) represents the fused 

 ganglia of the first six somites. The arrangement of its ganglionic capsules 

 is the same as in G. stagnalis and G. fusca (Figures 8, 10, 12, 18). The two 

 ventral capsules of somite vi. (6, 6, Figure 25) are arranged tandem, those of 

 somites i.-v., side by side. The supra-cesophageal commissure lies well back, 

 about over the lateral capsules of somite v. (Figure 26). 



4. Glossiphonia heteroclita Lixx.Ers (1761). 



Plate 5 ; Plate 8, Figs. 35, 36, 38. 



Hlrudo heteroclita Linnaeus (1761) ; H. hyalina O. F. Muller (1774); Clepsine 

 liyalina Moquin-Tandon ('26). 



a. Habitat, Form, Size, Color. 



This small and transparent leech is found both in Europe and in North 

 America. Compared with G. stagnalis and G. fusca, it has a proportioiKilly 

 shorter and broader body (Plate 5, Figures 19, 22 ;/ Plate 8, Figure 38. Com- 

 pare Plate 1, Figure 1 ; Plate 2, Figure 4) ; in its movements, it is less active. 

 It is found in ponds and sluggish streams, such as G. stagnalis frequents. 



Length of largest individuals, when extended, 13 nmi. ; at rest, 8-9.5 mm. 



Width, extended, 3 mm.; at rest, 4.25 mm. 



Color. — The body is in general verj' clear and transparent, like that of a 

 jelly-fish, but shows gieat individual variation in the matter of pigmentation. 



First, it always has more or less of a golden-yellow tint caused by the prcs- 



