CASTLE : NOKTH AMERICAN RHYNCHOBDELLID^. 49 



dent that the single pair of eyes found in each of the species stagnalis, fusca, 

 and elongata corresponds with the middle (largest) pair of eyes of this species, 

 the pair belonging to somite in. 



The oral sucker, as in the other species described, lies within somites i.-iv. 

 (Figures 29, 31). 



c. Eeproductive Organs. 



Male genital pore (po. ^, Figure 28), between somites xi. and xil. (rings 25 

 and 26), a position one ring anterior to that of the same structure in the 

 species already described. 



Female genital pore {po. 9 » Figure 28), between the second and third rings 

 of somite xii. (rings 27 and 28), the usual position of this structure in the 

 genus. 



Testes (te., Figure 28), ten pairs. The anterior six pairs occupy the same 

 positions as the testes in the species already described, being placed interseg- 



mentally in somites ' .' . The remaining four pairs occur immediately 



XIV. XIX. 



behind those already mentioned ; the most anterior one, between the last 

 crop and first stomach diverticulum, in somites — ' •, the other three between 



XX. 



successive stomach diverticula, and like them separated by rather less than 

 metameric intervals. No other species of Glossiphonia known to me, except 

 the European G. complanata, has normally a greater number of testes than six 

 pairs. In that species likewise the testes number ten pairs placed exactly as 

 in elegans. This is one of several facts showing the very close relationship of 

 the two species named. The last one or two pairs of testes are less constant in 

 their occurrence than those farther forward. 



Eggs are laid by G. elegans, in the vicinity of Cambridge, in April, May, or 

 as late as June. The temperature of the water in the spring undoubtedly 

 exercises considerable influence in determining the time of egg-laying. Indi- 

 viduals brought into the laboratory on March 27, 1898, laid eggs nine days 

 later. On April 29, 1900, animals of this species bearing eggs were collected 

 from Alewife Brook, Cambridge, though G. stagnalis, found with them, appar- 

 ently had not yet laid its eggs. The eggs are dull pinkish white in color and are 

 borne on the under side of the body in from three to six large clusters, which 

 are rather easily detached from the body, if the animal is disturbed. Each 

 cluster contains a considerable number of eggs, often as many as twenty or 

 twenty-five, enclosed in a delicate sac. The sacs are not arranged sym- 

 metrically in two parallel rows, as in G. stagnalis and G. fusca, but quite 

 irregularly, a sac being attached either in the median plane of the body or to 

 one side of it, as the case may be. 



d. Digestive Tract. 



The mouth is situated well forward in somite iii., anterior to the eyes, or at 

 least anterior to the last two pairs of eyes (Figures 29, 31). 



