A Lamellibranch. 57 



ing of the ureter, and the outer wall of the kidney is then 

 dissected away, the probe will be found to have reached 

 what is called the " upper limb " of the kidney. This cavity 

 is a comparatively smooth and thin-walled sac. It is con- 

 tinuous with the " lower limb" which lies posteriorly, and is 

 provided with more glandular walls. This lower limb finally 

 communicates, through a funnel-shaped opening, with the 

 cavity of the pericardium. The opening into the pericardial 

 space is small and somewhat difficult to demonstrate. These 

 renal organs are comparable to the nephridia of Nereis. 

 Make a careful drawing of the parts just studied. 



Reproductive System. The reproductive gland (testis 

 or ovary") is a somewhat delicate and voluminous organ, par- 

 tially enfolding the coiled intestine. The opening of its duct 

 has already been noted. 



The Nervous System. The left cerebral ganglion will 

 be found as a small body, about the size of a pin's head, 

 lying just behind the upper portion of the anterior adductor. 

 Find the short, transverse commissure that connects it with 

 its fellow of the opposite side. The visceral ganglia lie on 

 the lower surface of the posterior adductor. They are yel- 

 lowish masses, from which numerous nerves radiate. A 

 larger nerve may be followed from the left visceral to the 

 left cerebral ganglion. It is the cerebro-visceral connective, 

 and lies for the most of its extent near the surface. The 

 pedal ganglia lie side by side in the substance of the ante- 

 rior portion of the foot, and just below the visceral mass. 

 Cerebro-pedal connectives may be traced through the visceral 

 mass from the pedal to the cerebral ganglia. 



Make a drawing of the nervous system. 



