100 LABORATORY WORK. 



delicate tubular auricle * which brings the blood from the 

 gills to the ventricle. Notice the intestine passing through 

 the ventricle. Just in front of the posterior adductor is 

 the dark organ of Bojanus, or kidney. Draw the parts 

 made out. 



The alimentary canal and the nervous system are best 

 followed in specimens which have been in alcohol a few 

 days. In such a specimen insert a probe into the excur- 

 rent siphon. Notice that it does not enter the branchial 

 chamber. Cut through the thin membrane between the 

 gills of the right and left sides, posterior to the abdomen. 

 This lays open the cloacal chamber into which the probe 

 extends. In the dorsal wall of this chamber, just below 

 the posterior adductor, see a pinkish or orange body, the 

 parieto-splanchnic ganglion. From this trace backward 

 nerves which soon curve forward along the base of the 

 gills. Also trace two nerves forward, one on either side of 

 the body, until they meet in a pair of cerebral ganglia just 

 above the mouth. Are the two cerebral ganglia connected 

 directly with each other? From the cerebral ganglia trace 

 a pair of nerves downward to the pedal ganglia lying 

 between the abdomen and the foot. Sketch the nervous 

 system. 



Beginning with the intestine where it leaves the heart, 

 trace it posteriorly. On which side of the posterior adduc- 

 tor does it pass? Where does it empty? Trace it forward 

 from the heart, carefully picking away the surrounding 

 tissue with the needles, into and through the abdominal 

 mass, and plot the coils which it makes. It will be found 

 to pass into a rather large saccular stomach, on either side 



* The auricles are easiest seen in the fresh specimen by carefully 

 opening the pericardium and pouring in a little alcohol with a 

 pipette. This will harden and whiten its walls. 



