126 DISCOVERY REPORTS 



eggs, therefore, the distribution in time of each developmental stage may be spread over a period of 

 three months. Thus, eggs spawned in February may become adolescent in the foUow^ing September, 

 October or November, that is, specimens at stage 1 met with in these months may have originated 

 from eggs laid in February. Similarly, eggs spawned in March may become adolescent in the following 

 October, November or December, or alternatively, specimens at stage 1 in these months may have 

 developed from eggs laid in March and so on. 



The months, in which the other developmental stages may be theoretically expected to occur, can 

 also be worked out, by assuming that each stage lasts 2 months in the male and zh months in the 

 female. In this way, an explanation of the heterogeneous composition of the euphausian population 

 is obtained, and in Fig. 2 I have attempted to give some idea of this complexity at any given time by 

 a diagrammatic representation of the generations arising from the three batches of eggs, spawned in 



Table 17 



I 



February, March and April. The average length per month of each stage has been plotted, and the 

 points marking the maximum average values have been joined up, as well as those marking the mini- 

 mum average values. The space between has been hatched in colour: blue for the generation arising 

 from February eggs, red for March and green for April. The months in which the stages have been 

 calculated to occur, and the values of the average lengths are set out in Table 17. It will be noticed 

 that in the winter months no values are given for stage 5 in the males and stage 4 in the females. In 

 the scanty material available from this time of the year, these stages did not occur, although theoreti- 

 cally they should be present. In the figure the actual period of time, in which each stage appears, is 

 shown by a solid black line, the theoretical period by a broken line. 



The fate of early or late spawned eggs can be seen at a glance from the diagram. February eggs, 

 which have reached stage 1 at the beginning of the following season (i.e. September to November) 

 will have grown sufficiently to be at stage 4 or 5 before the winter sets in (i.e. June), and will be mature 

 by October or December of the succeeding spring ; they attain rather greater lengths than the later 

 generations. On the other hand, April eggs may not reach stage 1 until the following January, and will 



