28 



(4) Genital ducts. In the female these are a pair of 

 equally developed oviducts, which may be seen running 

 below the visceral epithelium from the urinary papilla 

 upwards for 12 to '24 mm., according to the size of 

 the specimen. The tip of the oviduct is alone free, and 

 protrudes for a short distance out from the visceral mass 

 into the mantle cavity, bearing the oviducal aperture at 

 its end, somewhat below the anterior end of the gill 

 (fig. 11, od. np.). In the male (fig. 8) 3 there is a single 

 genital duct — the penis situated similarly to tin 1 left 

 oviduct in the female (pen.). 



Other organs exposed on opening the mantle cavity. - 

 After removing the vertical septum the following are 

 seen : — 



(1) The intestine, running vertically up in the 

 median line, over the liver to the anus, with the anterior 

 vena cava lying on its left side ; 



(2) The ventral surface of the liver, covered by the 

 visceral envelope ; and 



(3) The two kidney sacs, posterior to the liver. 

 Visceral envelope. -On removing the epithelium and 



the septal muscle, which envelop the visceral mass of 

 Eledone, a muscular envelope external to this visceral 

 mass is exposed. ( )ver it ventrally run the visceral nerves 

 (PI. IX, fig. (>!), Visc.N.). This envelope, dorsally, runs 

 from the posterior bolder of the cerebral cartilage, to 

 which it is attached, down to the level of the branchial 

 hearts, where it becomes adherent to the muscular mantle. 

 The dorsal region of the envelope is stouter than the 

 ventral, and contains large widely separated chromato- 

 phores, which probably show through the mantle during 

 life. The thin ventral region covers over the liver and 

 ink sac, but is dorsal to the rectum. It runs back from 

 the ventral posterior edge of the cranial cartilage to the 



