BTTCCINUM. 341 



of the Monotocardia lies to the left side of the rectum, and 

 embiyological evidence supports strongly the view that 

 the ''kidney" of the whelk represents the left renal 

 organ of the Diotocardia. This conclusion seems at 

 present to be the most probable, and though in Patella it 

 is the left kidney that is reduced, the Docoglossa can 

 hardly be considered as on or near the line of evolution 

 of the Monotocardia. 



REPRODUCTIVE ORGANS. 



Under this heading will be considered: — (1) the 

 Gonads, (2) the Gonoducts, and (3) the organs of 

 copulation. The sexes are separate in Buccinum, as in 

 most prosobranchiate molluscs, and the difference is 

 well marked externally owing to the male possessing a 

 large penis which lies folded back in the mantle cavity. 

 The gonoducts are well differentiated and quite separate 

 from the renal organ, having their own openings to the 

 exterior. 



The Male Gonad (fig. 54, Go.), which resembles 

 the female in shape, size and appearance generally, is 

 situated upon the digestive gland and in close contact 

 with it. Both are in fact covered by the same membrane 

 forming the integument. The testis extends from the 

 cleft marking the point of contact of the two lobes of the 

 digestive gland, along the right side up to the very tip 

 of the spire (fig. 54). By reason of its more or less bright 

 yellow colour it stands out markedly against the dark 

 coloured tissue of the digestive gland. Slightly ventral 

 to the gonad on the right side, and on the surface of the 

 so-called " liver," so that it is visible to the eye without 

 any dissection whatever, runs the male duct, the vas 

 deferens (fig. 54, V. def.). It is at first very narrow, but 

 gradually increases in thickness as il approaches the 



