75 
is at the apex of a small papilla, and communicates with 
a sac in the interior. 
When resting, Lepeophtherus lies upon the ventral 
surface, keeping the first three pairs of feet moving with 
spasmodic jerks. When irritated, as in attempts to remove 
them from their host, the males and immature females 
move very rapidly over the skin of the fish. The mature 
females make no attempt to escape, only clinging more 
securely. On transferring them to clean sea water they 
settle on the sides and bottom of the vessel, and sometimes 
adhere to the surface film of the water, remaining quiescent 
for long periods. When the water is shaken slightly they 
detach themselves and swim about rapidly on their backs. 
They soon tire, however, and return to rest again. Lepeo- 
phtheirus makes no attempt to leave the water when kept 
in small aquaria. The allied form, Caligus, on the other 
hand, crawls out of the water and up the sides of the 
glass, where it remains, making no attempt to return, and 
soon dies owing to the evaporation of the water from 
under the carapace. These parasites are very tenacious 
of life, and live for a considerable time after the host has 
died if they are not allowed to dry up. In some instances, 
although the host had been dead over twelve hours, and 
the parasites to all appearance were also dead, they 
soon revived when placed in sea water. Increase of 
temperature to 16° C. and over is fatal to them. They 
can, however, stand very considerable decrease of tem- 
perature. On one or two occasions during February, 
1900, the small aquaria in the tank room at Piel, some 
of which contained parasites under observation, were 
frozen, and the temperature of the room itself stood at 
—1°C., but the parasites suffered no harm. They can also 
be kept alive in sea water for weeks without change if the 
aquaria are kept cool. 
