THE DEVELOPMENT AND LIFE-HISTORY OF 



ADOLESCENT AND ADULT KRILL, 



EUPHAUSIA SUPERB A 



By Helene E. Bargmann, ph.d. 

 (Text-figs. 1-3) 



INTRODUCTION 



^His paper is an extension of my short one, published in 1937- The stages in the development of 

 Tthe reproductive system described therein have been used here to work out the composition of the 

 euphausian population as a whole and its growth rate. This method was first employed by Ruud, 

 but as he was handicapped by lack of material he could not carry his work quite far enough. 

 I have been more fortunate in having access to the very extensive Discovery Collections; indeed, 

 there has been more material than I could cope with single-handed, and some selection became 

 necessary. My object has been to obtain as complete a series of observations as possible throughout 

 the whoL yelr. Unfortunately, weather and ice conditions in the Antarctic make it difficult to 

 fish nets in autumn and winter. The material for this time of the year is consequenUy very 

 scanty compared with that for the spring and summer months when there was such great 

 abundance that I could not examine it all. The voyages of the two ships R^R.S. D-o-ry 11 and 

 R R S 'William Scoresby', have covered between them the whole of the Antarctic zone, but the r 

 programme of work has kept them so continually on the move that regular observations in definie 

 LaUties are not available in consecutive months. I have therefore had to combine -tenal r m 

 different regions and different seasons in order to obtain records extending over all he months of he 

 year, and even so the material for the month of July is so scarce as to be neghgible. however 1 is 

 reasonable to conclude that, by using material for several seasons, a very fair general idea of the 

 average conditions in which Euphausia mperba grows and breeds is obtained. 



MATERIAL AND METHODS 



Material collected over a period of ten years was used. The me.ltod of examining specimens was the 

 same as that described in my previous paper. Each specimen was measured to .he nearest mrllune r 

 from the anterior margin of the eyes to the tip of the telson; the carapace was then opened under a 

 binocular microscope and the stage of development of the reproduct.ve system was determined, external 

 sexual characters also being noted ; 8029 specnnens were measured and dissected ,n this way. 



The results of th,s intenL investigation are all set out in the appendix. The total catch from each 

 station has been divided into males and females, which are tabulated separately. All particulars of 



ngth and internal and external development are given, together with the totals of the different stages. 

 Frfser's records of eggs and early larvae have been added .0 the lists of females to show as clearly as 

 possible the correlation between the occurrence of adults and eggs. t.t j-ff„.„, 



' No statistical tests of validity have been applied to calculations of the average lengths of the different 

 stages, because the stages are in themselves always anatomically distinct. Nor have any fortnulae been 

 used in working out the curve of growth. There are too many factors involved for any of the existing 

 mathematical tfethods to be applied with any certainty. As Ottestad (1933) writes: "In the course of 



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