MOLLUSC A 



of muscle fibres ; it opens into the left and right aortae, the 

 former supplying the circular muscle. Both aortae soon termi- 

 nate in lacunar spaces, from whence the blood presumably 

 passes to the gills. The blood is colourless, and contains 

 amoeboid corpuscles. 



The nephridia are paired, but the right is much larger 

 than the left. They open to the exterior by small renal 

 papillae, situated one on each side of the anal prominence, and 

 also, according to some observers, internally by two minute 

 pores into the pericardium. The existence of the reno-peri- 

 cardial openings has recently been denied, both in Patella and 

 in Fissurella. Haliotis and Trochus possess a left reno-peri- 

 cardial duct only. The left kidney lies between the rectum 

 and the pericardial chamber. The right kidney, which is 

 aborted in other Anisopleura, occupies a large space in the 

 visceral hump. In part of its course it is closely applied to 

 the generative organs, and when the ova and spermatozoa are 

 ripe they are stated to burst into the lumen of the kidney, and 

 so to leave the body through the renal papilla on the right of 

 the anus. The lumen of the kidney is much broken up by 

 ridges which project into it from its walls. The ridges are 

 covered with glandular epithelium, which is partly ciliated ; in 

 the substance of the ridges numerous blood-vessels ramify. 



The nervous system is very complex, it comprises several 

 pairs of ganglia, the most important of which are the cerebral, 

 the pedal, and the pleural. The cerebral ganglia are situated 

 at the base of the tentacles, they give off nerves to the eyes 

 and to the tentacles. The two ganglia are united by a com- 

 missure above the pharynx ; they also give off a commissure on 

 each side which passes to an anterior superior buccal ganglion. 

 From each buccal ganglion two commissures arise, one uniting 

 it with the similar ganglion of the other side, the other pass- 

 ing posteriorly to a posterior superior buccal ganglion, which is 

 in its turn united with the similar one on the other side. Thus 

 the buccal nervous apparatus consists of a square of commis- 

 sures with a ganglion at each angle. The cerebral ganglia are 

 connected with one another by a commissure which runs 

 underneath the buccal mass ; this bears two small ganglia — the 

 inferior buccal ganglia. 



