82 ANNELIDA. 



find the nephrostome. Remove a nephridium by means of fine 

 forceps and examine it with a microscope. 



Reproductive System. The sexes are separate, but no per- 

 manent gonads are present. At the breeding season the ova 

 or spermatozoa are proliferated from the ccelomic epithelium 

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

 body-wall. 



Nervous System. 1 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. 



Lillie: Studies of Fertilization in Nereis. I and II. Jour. Morph., 22, 1911. 



III. and IV. Jour. Exp. Zool., 12, 1912. 

 Mayer: The Annual Breeding-swarm of the Atlantic Palolo. Carnegie 



Inst. Pub., 102, 1908. 

 E. B. Wilson: The Cell-Lineage of Nereis. A Contribution to the Cytology 



of the Annelid Body. Jour. Morph., 6, 1902. 

 Woodworth: The Palolo Worm, Eunice viridis. Bui. Mus. Comp. Zool., 



Harvard, 51, 1907. 



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 



1 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 parappdia should be made in a mixture of glycerin and ammonium 

 picrate solution. 



