TRANSVERSE SECTIONS 101 



b. The ureters are a pair of thin-walled tubes lying 

 along the dorsal surface and outer sides of the 

 kidneys, immediately below the pericardium. 

 They are separated from each other in the median 

 plane by the vena cava. 



7. The nervous system. 



The connectives between the cerebral and osphra- 

 dial ganglia lie side by side, between the two kidneys 

 and immediately below the vena cava. 



C. Transverse Section through the Middle of the Posterior 

 Adductor Muscle. 



1. The posterior adductor is a large mass of transverse 



muscular bands running across the dorsal part of the 

 section. 



2. The gills are cut across close to their hinder ends, and are 



small. The inner lamellae of the two inner gills are 

 united with each other in the median plane, forming a 

 . horizontal septum which separates the large branchial 

 chamber below from the wide but shallow supra- 

 branchial or exhalent chamber. 



3. The rectum lies immediately dorsal to the adductor 



muscle. The typhlosole is still present. 



4. The osphradial ganglia lie side by side on the ventral 



surface of the adductor. 



