SEA-FISHERIES LABORATORY. 291 



departure from the normal in the number or structure of 

 the nephridia. After examining these organs in a 

 general way, carefully remove the oblique muscles which 

 cover one or two of the nephridia and examine these with 

 a lens, noting the various parts. Note the funnel, its 

 dorsal lip fringed with processes, its ventral simple lip, the 

 excretory portion of the organ, the bladder, the gonad (not 

 present on the first nephridium), the blood supply, &c. 

 At the breeding season the vesicles may be distended with 

 ripe ova or spermatozoa. Remove one of the nephridia 

 entire and transfer it, with as little disturbance as pos- 

 sible, to a glass slide and examine under the microscope. 

 If the worm has been freshly killed the strong action of 

 the cilia of the funnel will be well seen. Note the vessels 

 of the funnel, some of which have blind dilated endings. 

 Note also the gonad traversed by the gonidial vessel. The 

 excretory portion of the organ may be cut across ; at the 

 cut edges the action of the long cilia borne by the cells of 

 this portion may be seen. 



VI. Nervous System.— The greater part of the 

 ventral nerve cord may be easily seen on pushing the 

 alimentary canal to one side. It may be readily traced 

 forwards as far as the first diaphragm, but the rest of the 

 cord, the connectives, the brain and the otocysts are only 

 exposed after the first diaphragm has been carefully cut 

 away from the body wall. Very little further dissection 

 is required. It is often, however, an advantage to cut 

 away the pharynx, as shown in fig. 46. The exposure of 

 the brain requires some care. The otocysts are usually 

 rather yellowish bodies about the size of a small pin's 

 head, their position is seen in fig. 46. Remove an otocyst 

 to a slide, cover it and examine it under the microscope. 

 The peculiar quivering motion of the otoliths will be seen 

 if the specimen has been only recently killed. 



