INTRODUCTION. 5 



naked eye. In others the cephalic segment becomes 

 highly chitinised, and is frequently expanded into 

 horn-like processes which are buried in the tissues of 

 the host. Certain members of the Caligoida are able 

 to live apart from their hosts and lead a more or less 

 pelagic life in the water for a time, but whether adult 

 females voluntarily detach themselves from healthy 

 and living hosts is doubtful. They appear, however, 

 to leave the host when it dies in an aquarium tank. 

 One rarely finds LepeopJitheirus pectoralis on dead 

 flounders which have been allowed to remain in a tank 

 for a day or two after death, although it was quite 

 certain they were present when the host was alive. 

 We have kept Lepeophtheirus pectoralis alive in vessels 

 of sea- water for periods of six weeks after removal from 

 flounders. Adult males of C aligns rapax are often 

 met with in collections of plankton, but the females 

 are less frequently noticed. The members of the 

 genera Chondr acanthus and Olavella sometimes live for 

 a couple of days after being removed from their hosts, 

 but the Lernaea quickly perishes. It is almost certain 

 that, with the exception of a few members of the 

 Caligoida, all the copepod parasites of fishes die soon 

 after the death of their host, even although the body 

 remains in the water. On one occasion we dissected 

 the spiracles of a large grey skate (Raia batis) which 

 had evidently died in the sea and was afterwards 

 washed up partly macerated on the beach. A full- 

 grown specimen of Charopinus dalmanni was found in 

 one of the spiracles and was in a perfect condition, 

 but there was no sign of life in it. 



The sexes are separate, the males as a rule being 

 much smaller than the females. In many cases the 

 males are simply parasites on the females, especially 



