88 ANNELIDA. 



Circulatory System. — This system is very difficult to ob- 

 serve. Dorsal and ventral blood-sinuses are present, and com- 

 municate anteriorly by a circular sinus. 



Excretory System. — Find a pair of brown ncphridia, an 

 inch or more in length. Cut off a nephridium (from the fresh 

 worm) as close as possible to the body-wall, and examine it 

 under a microscope. Near the cut (the attached) end find the 

 coelomic opening or nephrostome. Is it ciliated? 



Reproductive System. — The sexes are separate. There 

 are no permanent gonads, but at the breeding season sex-cells 

 are proliferated from the coelomic epithelium, at the points where 

 the ventral retractor muscles are attached to the body-wall. 

 These cells become detached and mature while floating in the 

 coelomic fluid. They pass out through the nephridia, which 

 function as gonoducts. 



Nervous System. — Does the ventral nerve-cord seem to be 

 double? Is it ganglionated ? Does it give off lateral nerve 

 branches? Trace the circum-esophagcal connectives to the supra- 

 esophageal ganglion. The ganglion is small and situated behind 

 the tentacular fold, to which sensory nerves extend. Does any 

 system of organs show segmentation? 



Make a drawing to show the internal anatomy. 



