114 



DISCOVERY REPORTS 



The smallest specimen at stage 2 occurred in December and measured 20 mm. ; the largest mea- 

 sured 48 mm. and occurred in February. The first was at stage A in external development, the second 

 at stage C. The six specimens recorded at stage E measured from 38 to 42 mm. Most of these adoles- 

 cents, however, were at stage B: 679 specimens were examined and it was found that 157 were at 

 stage A, 346 at stage B, 138 at stage C, 32 at stage D and 6 at stage E. The average length varied from 

 29 mm. in August through 25 mm. in November to 38 mm. in March, falling to 36 mm. in June. 



Of stage 3, 458 specimens were examined. Only two of these were external at stage A; of the rest, 

 130 were at stage B, 158 at stage C, 146 at stage D and 22 at stage E. The average monthly length 

 varied from 35 mm. in August to 43 mm. in March, falling again in April to 40 mm. and rising once 

 more to 41 mm. in May and June. Great variation in the individual length of the specimens is met 

 with again and, as in stages 1 and 2, the largest measurements approach the average lengths of the 

 young adults very closely, showing that in the female adolescents, as in the male, size is no reliable 

 criterion of development. The smallest specimen was recorded in October: it measured 22 mm. and 

 was at stage C externally. The largest specimens occurred in February and June: they measured 

 49 mm. and were at stages C and E respectively. 



The females now approach maturity. At the next stage (4), the eggs become measurable although 

 the ovary is only half-grown, and in some specimens spermatophores are found in the thelycum, 

 showing that externally these females are fully mature. I regard stage 3, therefore, as marking the 

 end of the period of adolescence in the female. 



ADULT KRILL 

 MATURE MALES 



There are two adult stages in the male, stages 6 and 7. In both, spermatophores are to be found in 

 the ejaculatory ducts, but in specimens at stage 6, the spermatophores are not perfectly formed, whereas 

 when stage 7 is reached, there are fully formed spermatophores in both the ejaculatory ducts and in 

 the spermatophore sacs. Two adult external stages in the development of the copulatory organs can 

 also be distinguished. These stages are tabulated below; they correspond to stages 2, 3 and 4 of Ruud. 



Table 8. Growth stages in adult males 



The average monthly length of stage 6 ranged from 44 mm. in August, through 41 mm. in Novem- 

 ber, to 54 mm. in February, falling again to 52 and 51 mm. in March and April. Between May and 

 August, no specimens at this stage were found. The smallest specimen, measuring 35 mm. occurred 

 in November, and the largest specimen measuring 64 mm. in February. The November specimen was 

 at stage G externally, and the February specimen was at stage F. In all, 192 specimens were examined, 

 6 being at stage D, 4 at stage E, 124 at stage F and 58 at stage G. 



No fully adult specimens at stage 7 were found in May, June and August, and only one specimen 

 was found in July. The average monthly length varied from 54 mm. in September, through 44 and 

 45 mm. in October and November to 52 mm. in February, March and April. The smallest specimens, 



