Parasitic Copepod Thersitina gastero3tei. 417 



female. The large size of the receptaculum seminis also 

 seems to confirm this conclusion. No males are to be found 

 at the time when reproduction first becomes active in the 

 spring, so that the spermatozoa must remain alive within the 

 female for about five months. 



I have no observations for November or December, but in 

 January neither larvse nor egg-bearing females are to be 

 found. Reproduction first becomes active about the beginning 

 of March, and continues throughout the summer. There 

 seems to be a distinct periodicity, indicating, as I believe, a 

 series of five generations within the year, though, of course, 

 these generations will to some extent overlap and obscure 

 one another. I suppose that a mature female lays two, or 

 perhaps three, lots of eggs, and then dies and gives place to 

 the new generation. The general course of events is, I 

 think, as follows : — 



January. — Period of rest. No eggs. No larvfe. 



March. — Reproductive period begins. Nauplii to be found, 



but no later larvae. 

 April. — Larvce mature, and fix themselves towards end of 



month. 

 May. — Disappea: ance of the winter generation ? Egg-laying 



of new (first) generation hatched in April. 

 June. — Fixing and maturing of adults continue and some 



begin to hatch eggs. 

 July. — No observations, but probably the second generation 



hatched in June breed and their larvaa mature. 

 August. — Third generation fix and produce young, so that at 



end of month the fourth generation is nearly ready to 



fix. 

 September. — No observations. Probably fixing and ripening 



of fourth generation. 

 October. — Fourth generation still living, but ceasing to breed. 



Fifth generation fixing and beginning to mature. 

 November and December. — No observations. Probably a 



resting period, without production of eggs. 



Structure of the Adult. 



The general form of the adult female has already been 

 adequately described *, but no account of the male lias, so 

 far as I am aware, been given. The male described and 



* Scott, Eighteenth Ami. Rep. Fishery Board for Scotland, part iii 

 1900, p. 14G. 



