36 bulletin: museum of comparative zoology. 



h. Rings, Somites, Eyes, Suckers. 



External rings, not quite so distinct as in G. stagnalis ; skin, slightly roughei 

 owinCT to the stronger development of Bayer's ('96) sense organs. Number of 

 preanal rings, seventy (Figure 13, Plate 4). 



Somites v.-xxiv. are triannulate, but the two anterior rings of v. are united 

 ventrally (Figure 15). 



Somites i. and ii. are included in a single broad ring, which, just as in G. 

 stagnalis, is sometimes subdivided by a shallow transverse furrow (Figure 14) 

 marking the boundary between the two incompletely fused somites. 



Somites iii., iv., xxv. and xxvi. (Figures 13-16) are biannulate. In each 

 case the broader, anterior ring bears the sensillae and corresponds to rings 1 and 

 2 of triannulate somites (compare somites iv. and v. of Figure 15). 



Somite xxvii. is a single broad ring (70, Figure 13) which lies just anterior 

 to the anus, not crowded back of it, as in stagnalis (Figure 34, Plate 8). 



The principal diflferences in somite composition between fusca and stagnalis 

 occur in the head region, in somites iii.-v. These somites are less abbreviated 

 (or more fully elaborated) in fusca than in stagnalis, hence the greater number 

 of preanal rings in the former (seventy) as compared with the latter (sixty- 

 seven). 



Eyes, two, large and distinct, situated in rings 3 and 4 (Figures 14-16). 

 The sensory elements of each eye, as in G. stagnalis, are contained in a pig- 

 ment cup which is open only on its anterior, lateral surface, where the nerve 

 fibres make their exit (Figures 14, 16). 



Oi-al sucker, as in all species of Glossiphonia, included within the first four 

 somites (Figures 14, 15). 



Posterior sucker of about the same dimensions as in G. stagnalis, slightly 

 longer than broad. 



c. Reproductive Organs. 



Male genital pore (po. $, Figure 13), between the first and second rings of 

 somite xil. (rings 27 and 28). 



Female genital pore {po. 9. Figure 13), between the second and third rings 

 of somite xii. (rings 28 and 29). 



Testes (te.. Figure 13), six pairs situated intersegmentally in somites 



XIII. XVIII. 



XIV. XIX. 



The ovaries have the usual form and position of these structures in other 

 species, being found ventrally in the median lacuna. 



Eggs are laid a month or six weeks later than by G. stagnalis (June 12, 

 1898, Cambridge, Mass.). In color they resemble those of G. stagnalis closely, 

 being of a light pink or flesh color. As in G. stagnalis, the eggs are attached 

 to the under side of the body posterior to the genital pores, within a number 

 of delicate sacs arranged in two parallel rows, close together, one on each side 

 of the median plane. The numbiT of sacs is most often six, but a seventh sac 



