94 ANNELIDA 



find the minute pear-shaped nephridia. Determine their dis- 

 tribution in the body. Each nephridium consists of a tor- 

 tuous canal in a multinucleate mass of protoplasm. The 

 external opening is the nephridiopore above mentioned. The 

 inner end perforates the septum anterior to the body of the 

 nephridium and opens into the coelomic cavity of the seg- 

 ment next in front, by a ciliated funnel, the nephrostome. 

 With a hand lens try to 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 

 permanent gonads are present. At the breeding season the 

 ova or spermatozoa are proliferated from the coelomic ep- 

 ithelium of a large number of segments and escape by rup- 

 ture of the body wall. 



Nervous System. 1 — On lifting the alimentary canal you 

 will see the ventral ganglionated nerve cord. Note the nerves 

 passing off laterally from the ganglia. How many pairs of 

 nerves per segment are there, and how are they placed? Are 

 the ganglia 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 

 circumesophageal connectives which unite above in the bi- 

 lobed brain or supra-esophageal ganglia. Sensory nerves con- 

 nect the brain with the eyes, tentacles, and palps. 



Make a drawing of the nervous system. 



Binard et Jeener: Morphologie du lobe preoral des polychaetes. Inst. 

 Zool. Torley-Rousseau Recueil (Bruxelles), 2, 1928. 



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

 with needles in a specimen which has been macerated in 20 per cent 

 nitric acid for twenty-four hours. Sensory cells and their neurites can 

 be identified in the parapodia by placing them in a 1 per cent solution 

 of ammonium picrate after having let vigorous worms crawl around for 

 three or four hours in a small amount of 1 per cent solution of meth- 

 ylene-blue. Mounts of the parapodia should be made in a mixture of 

 glycerin and ammonium picrate solution. 



