74 ANNELIDA. 



or spermatozoa are proliferated from the ccelomic epithelium 

 of a large number of segments and escape by rupture of the 

 body- wall. 



Nervous System.^ — On lifting the alimentary canal you will 

 see the ventral ganglionated nerve cord. Note the nerves pass- 

 ing off laterally from the ganglia. How many pairs of nerves 

 per segment are there, and how are they placed? Are the gan- 

 glia metameric? Is there any indication that the nerve cord is 

 double? At the anterior extremity of the cord note the infra- 

 esophageal ganglia and, extending from them and encircling the 

 anterior end of the alimentary canal, the circum-esophageal con- 

 nectives which unite above in the bilobed brain or supra-eso- 

 phageal ganglia. Sensory nerves connect the brain with the eyes, 

 tentacles, and palps. 



Make a drawing of the nervous system. 



LUMBRICUS. (Earthworm.) 



Earthworms feed mostly at night. What reason is there 

 for this habit? You should look for earthworms with a lantern 

 some mild, calm summer evening when the ground is quite 

 moist. See if they leave their burrows entirely. How much 

 of the body is generally protruded? Can you determine what 

 the worms are doing? Are they disturbed by walking near 

 them? Are they ever disturbed by flashing the light suddenly 

 upon them? Of what service to them is the ability to distin- 

 guish light? Look for castings near the burrows. During day- 

 light look for castings and thus determine the relative abundance 

 of worms in lawns, gardens, etc. (As the worms come to the 

 surface only when it is moist, castings will be abundant onlv 

 at such times.) Do the castings indicate anything about the 

 feeding habits. 



^ The nervous system can be most readily studied by tearing it out with 

 needles in a specimen which has been macerated in 20 percent nitric acid 

 for twenty-four hours. Sensory cells and their neurites can be identified 

 in the parapodia by placing them in a 1 percent solution of ammonium 

 picrate after having let vigorous worms crawl around for three or four 

 hours in a small amount of 1 percent solution of methylen-blue. Mounts 

 of the parapodia should be made in a mixture of glycerin and ammonium 

 picrate solution. 



