208 
these may have an important bearing on the parasitic 
diseases of some of our food fishes. 
Directions ror Pracricat 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 1s sometimes so strong as to cause rupture of 
the body wall, in which case the ccelomic 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 55 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 chetigerous 
portion,’ middle branchiate chietigerous region and pos- 
terior achietous and abranchiate tail; the segmentation ; 
