jj^ DISCOVERY REPORTS 



In the immediately post-larval female the ovary is unlobed and saddle-shaped. Growth takes place 

 steadily, the ovary becoming lobed and extending ventrally on to the thoracic muscles and posteriorly 

 into the abdominal region. Development of the thelycum takes place simultaneously with the growth 

 of the ovary and by the time the thelycum reaches the adult shape and is heavily chitinized the ovary 

 is usually touching or overlapping the thoracic muscles and the shell gland is just starting to develop. 



Eggs were measured under a low power binocular microscope in io8 E. triacantha at various stages 

 of maturity, the smallest female in which this was possible being 20 mm. in length and in which the 

 eggs were 0-05 mm. in diameter. The smallest female E. superba in which Bargmann (1945, p. 115) 

 found eggs of this size was 27 mm. When they can first be measured all the eggs on the dorsal surface 

 of the ovary are of uniform size, but as the ovary matures the eggs in the region of the oviduct increase 

 in size more rapidly than the others and it is in this region that the largest eggs are always found. 

 At a slightly later stage the eggs near the tips of the lobes enlarge and a graded series is formed from 

 the median part of the ovary where the eggs are small to the outer edges of the lobes where they are 

 large. However, even in the most mature female examined, in which the largest eggs measured 0-44 mm. 

 and were opaque and yolky in appearance, there still remained a narrow border of small eggs (0-05 mm. 

 diameter) round each of the lobes, and it is probable that these eggs never develop any further. Only 

 two females have been taken which give the appearance of having spawned. However, in one of these 

 the thelycum contained two full spermatophores and in the other, one full and one damaged sperma- 

 tophore. In both these the ovary had the original saddle-shape described by Bargmann (1937, 

 p. 348) for spawned E. superba and the oviducts could be seen as wide flat bands whereas in the young 

 stages with this type of ovary they are narrow. 



Out of eighty-five female E. triacantha carrying spermatophores fifty-three were full, ten half-full 

 and fourteen empty. The remaining eight carried one full spermatophore, the other having been 

 broken oJBF, and these can probably be included with those with full spermatophores. Although these 

 numbers are small this suggests that the sperm-mass remains in the spermatophore for some consider- 

 able time before migrating into the thelycum. It is interesting to compare this with Bargmann's 

 observation (1945, p. 117) that 'of 556 females {E. superba) carrying spermatophores, only 102 were 

 full, showing that the migration of the sperm-mass into the thelycum must be a rapid process '. 



Growth rate 

 The life cycle of E. triacantha takes two years to complete as in E. superba (Ruud, 1932; Bargmann, 

 1945). This is shown in Fig. 15 in which the data from hauls down to 500 m. with the NiooB and 

 N70V have been used to plot the length frequencies for each month of the year. The animals have 

 been divided into two-millimetre groups and the number in each group expressed as a percentage 

 of the total number measured in each month. These totals are shown at the top of the figure. In 

 calculating the larval frequencies measurements have not been made ; instead it has been considered 

 sufficient to use the mean length for each stage shown in Fig. 13 (p. 331). In view of the fact that the 

 data have been taken from many different localities in different years the results presented in Fig. 15 

 are remarkably consistent, and this suggests that there is little variation in the rate of growth from 

 region to region and from year to year. 



In September three distinct size groups can be seen: the larvae, which result from a recent spawn- 

 ing, the adolescents, which were spawned in the previous year, and the adults, spawned two years 

 previously and now due to spawn themselves. The larvae in September consist entirely of first calyp- 

 topes. In the succeeding months the young stock is gradually built up, the predominant stages being 

 first and second furcilia in November (about 4-6 mm.), second and third furcilia in December and 

 fourth to seventh furcilia in January and February. By April nearly all the o-year group have become 



