THE OSTEACODA. 



309 



male), the fact that it was taken at great depths, wliile no female was captured below 

 100 fathoms, points to something very unusual about the domestic arrangements of this 

 species. 



The Death-rate. 



I had hoped to be able to work tliis out in several species from the actual numbers 

 captured at successive stages. But there was only one species which fulfilled the 

 necessary conditions for such a study — that it was large, plentiful, and with all its stages 

 represented habitually in the epiplankton *. This species was naturally magna, and it 

 is remarkable how its numbers are related. The following are the actual numbers 

 measured and sexed : Stage I., 159 ; Stage II., 337 ; Stage III., 675. Now 675 -2 = 337, 

 and 337 -i- 2 = 168. That is to say, the total at each stage when halved yielded approxi- 

 mately the total for the next highest stage ; or, in other words, tlic death-rate was 

 50 per cent, at Stages II. and III. 



The ratio may be a mere coincidence : it takes for granted that reproduction had been 

 going on at a uniform rate for some time — a condition which was obviously not the case 

 in some other species. But the observation seems worth putting on record. 



* The latter necessary, owing to the impossibility of direct comparison between the closing-nets and the others. 



49* 



