THE DEVELOPMENT AND LIFE-HISTORY OF KRILL 



119 



Table 12 {co7it.) 



Using these figures as a guide, I then analysed the egg measurements from all the available material 

 (839 females)/ and I found that the eggs could be conveniently classified into four size groups, these 

 groups being used to differentiate the four internal stages in the adult females, stages 4-7. The first 

 group includes eggs measuring between 0-05 and 0-12 mm., with a mean diameter at o-o8 mm. 

 (class i); the second, eggs measuring between 0-13 and 0-24 mm., with a mean diameter at o-i8 mm. 

 (class 2); the third, eggs measuring between 0-25 and 0-48 mm., with a mean diameter at 0-36 mm. 

 (class 3) ; and the fourth, eggs measuring between 0-49 and 0-70 mm., with a mean diameter at o-6o mm. 

 (class 4), at which size the females are gravid and spawning occurs. 



The analysis of these egg measurements, set out in Table 12, shows that, at first, development is 

 slow, but that, as the season advances, a steady rate of growth ensures that the eggs approximately 

 double their size each month, and take about four months to reach maturity. 



The first measurable eggs occurred in females taken in August, and the majority of eggs in August, 

 September and October were in class i. In November, class 2 appeared in larger numbers and was 

 at a maximum in December. Class 3 appeared for the first time in any quantity in December and was 

 at a maximum in January. Class 4 was at a maximum in February, and in this month and in March 

 and April, the bulk of the females had spawned. 



It will be noticed that in March the mean diameter of the eggs has dropped to the same figure as 

 in August and October, the majority of the females having spawned and those with measurable eggs 

 being mostly in class i. Again, in April, apart from the females which have spawned, there is a range of 

 small eggs. It is possible that these eggs never mature. I have found no females with measurable eggs 

 during the winter months of May, June and July, nor any full adults which have spawned. This mav 

 be due either to the sparse material from this time of the year, or else to the fact that the adults do not 

 survive the winter. One particularly striking fact emerges from this analysis of egg measurements: 

 class 4 containing gravid females is represented by very small numbers. The problem of the depth at 

 which spawning takes place has already been discussed, as having a possible bearing on the absence 

 of gravid females from the catch. 



The evidence from these egg measurements points to a spawning season extending from January 

 to April, an increasing number of females having laid their eggs as the season advances. But if the 



* These measurements are given in full in Table 20 in the appendix. 



