74 Pub. Puget Sound Biol. Sta. Vol. 2, No. 36 



are very active. They swim about with a snappy, spiral dart. In this 

 condition they may exist for about two days, constantly searching for a 

 host to which to attach themselves. If the larva cannot find a host it 

 soon dies ; if it comes in contact with one it attaches itself and undergoes 

 further development. 



Each larva possesses powerful mouth parts and a peculiar attach- 

 ment filament. When the louse comes in contact with a desirable portion 

 of the fish, it first rasps a hole by means of its mouth parts. Then it 

 brings the attachment filament in contact with this cavity and injects tke 

 mushroom-like knob into it. The attachment filament is supplied with a 

 glue-like substance, which makes the organ adhere to the flesh of the host. 

 Furthermore, the regenerating tissue of the host fastens the parasite more 

 securely. The organism then begins to feed, increases enormously in size 

 and undergoes degeneration. 



In about two weeks after attachment, the copepod is ready for fer- 

 tilization. The male is only about one-third the size of the female. When 

 mature the male releases his hold on the fish, seeks out the female and 

 attaches himself to the posterior extremity of her abdomen, near the 

 reproductive organs. Here the male pastes a pair of elliptical pouches 

 known as spermatophores. These are filled with spermatozoa, which be- 

 come stored within the female's body and are later used for fertilizing the 

 mature eggs. At the time of the ripening of the eggs two long cigar-like 

 sacs are developed from the posterior margin of the female's abdomen. 

 These are the egg-sacs ; and it is here that the embryos undergo their 

 complete development. It takes about a month for the young free-swim- 

 ming larvae to hatch from these structures. 



After fertilization the male dies, while the female lives on to complete 

 the life-cycle. The female increases enormously in size, becomes very 

 degenerate and produces a great many young. In Salmincola edwardsit 

 two sets of young are developed, one lot containing about 120 embryos, 

 whereas the second one is somewhat smaller in number. The female dies 

 soon after all the eggs are liberated. 



The naturally crowded conditions of the fish witliin the hatcliery 

 })onds makes it very easy for the fish-lice to find their hosts and the loss 

 is therefore enormous. The young fish (Fig. 1) as well as the adults are 

 here attacked, but it is mainly the adults which are parasitized. The 

 adult fish are attacked b}' such numbers of the pests that they are ulti- 

 mately killed. As many as 250 copepods may be picked off one trout. 

 The injury produced in such cases is very great. The blood of the host 

 is removed in enormous quantities ; thus the fish is literally starved. The 

 injury produced to the host when the parasite attaches itself causes the 



