288 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



these may have an important bearing on the parasitic 

 diseases of some of our food, fishes. 



Directions for Practical Work. 



Arenicola should be dissected as soon as possible after 

 it is taken from the sand, and especially in warm weather, 

 as the animal soon dies and changes rapidly take place in 

 both the external and internal structures. Specimens at 

 least eight or nine inches long should be obtained if 

 possible ; the large Laminarian variety is excellent for 

 dissection. 



Specimens intended for dissection may be killed by 

 placing them in sea water in a jar and adding sea water 

 which has been shaken up with chloroform. By this 

 method the specimens are gradually narcotised, and they 

 usually die in a moderately expanded condition. If the 

 process of killing be too rapid, as, for example, if the 

 worms were dropped into chloroform, the contraction of 

 the muscles is sometimes so strong as to cause rupture of 

 the body wall, in which case the coelomic fluid is lost and 

 a considerable portion of the alimentary canal is forced 

 out through the opening, and some of the blood-vessels 

 may give way. As soon as the specimens are dead they 

 should be transferred to the dissecting dishes containing 

 sea water. If ordinary sea water^be not available make 

 up beforehand a sufficient quantity of artificial sea water 

 by adding about 35 grammes of sea-salt to each litre of 

 fresh water required. 



External Characters. — Note the shape of the worm; 

 its division into an anterior abranchiate chsetigerous 

 portion, middle branchiate chsetigerous region and pos- 

 terior achaetous and abranchiate tail ; the segmentation ; 



