HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 365 



larval and immediately succeeding adolescent components, the latter as Fraser (1936, p. loi) points 

 out, unlike the larvae, exhibiting no hard and fast developmental characters. ' Attempts ', he says, 

 'which were made to arrange the adolescents in groups of stages dependent upon the number of 

 setae on the antennal scale did not yield any satisfactory results, and it was made obvious by inspection 

 of the animals that in other appendages as well no hard and fast pattern of development exists '. The 

 developmental condition of mixed larval and adolescent swarms can only be determined, therefore, 

 short of an enormous series of dissections, by measurement, and so in the diagrams representing the 

 condition of the young winter and spring swarms, while staging continues to be adopted (in so far as 



AUGUST 



SEPTEMBER 



OCTOBER 



NOVEMBER 



2a 

 26 

 24 



22 

 20 

 16 

 16 

 14 

 12 

 10 

 8 

 6 



28 28 29 29 29 29 29 4 4 13 13 17 17 17 r? 17 17 18 18 IB 18 19 19 19 19 5 5 6 6 6 6 6 6 7 7 7 7 29 29 I I I I 2 2 17 17 17 17 



W26I W266 W267 W26BW276 W279W280W2B2W283 W2a5 W286 W2g7 W2e8W300W302W303W2O4W305W3a7 4W 471 472 2478 488 491 



W264W266 W257 W276 W279 W280W282W2B3 W285 W2B6W287 W288W300W302W303W304W305W3C7 469 471 472 2478 488 491 



Scale per cent 



' ' ' ' ' ' H FURCILIA 6 \//i'/. 



ADOLESCENT 



2B 

 26 



22 U> 



20 I 



18 " 



,6 f 



14 g 



12 1^ 

 lO 



B 



6 



N2 EXAM- 



- INED 



75 30 79 47 25 35 24 67 75 40 41 42 56 63 73 41 32 38 28 75 70 62 61 48 69 

 35 20 21 34 65 26 33 25 60 57 60 44 37 27 36 68 62 36 34 30 38 39 27 31 



NS EXAM- 

 -INED 



Fig. 114. Length frequencies of larval and adolescent components of young winter and spring swarms showing heavy 

 contribution of the last larval stage to the small (11-20 mm.) food of the whales. For vertical scale see legend to Fig. 107. 



mere separation into larvae and adolescents can be called staging), the length frequency of the sample 

 has been presented graphically in every instance where the latter was determined. Both winter and 

 spring diagrams then show not only the developmental condition of the surviving larvae, but also 

 that of the small whale food, or 11-20 mm. class, to the mass of which the Sixth Furcilias provide 

 a major contribution. The heavy extent of this contribution, especially from September onwards, is 

 illustrated in Fig. 114, which, except for one instance (Station 2478), is based throughout on the 

 measurements and larval and adolescent determinations published by Fraser (1936, Appendix i). In 

 this diagram 49 young winter and spring swarms have been separated into their larval and adolescent 

 components, the length frequencies of each component in 2-mm. groups being shown side by side 

 for comparison. Only stations at which 20 or more individuals of each component were measured 

 are shown. Besides showing the degree of overlap in length frequency of the two components 

 Fig. 114 also illustrates how typically, notably in September and October, the Sixth Furcilia does not 

 moult and become adolescent until it reaches a length of 1 1-12 mm. In fact, as represented here, the 

 transition from last larval stage to adolescent is disclosed as a thing of some abruptness, losing, in the 

 2-mm. length grouping, some of the indefinite merging of one developmental phase into another upon 

 which Fraser comments. For instance, in August the majority of the young individuals of 10 mm. 

 and under, are larval, and the majority of those of 1 1 mm. and over, adolescent. Again, in September, 

 October and early November there occurs repeatedly an abrupt step from 12 mm. and under, majority 

 larval, to 13 mm. and over, majority adolescent, and in November (in some instances) a jump from 

 14 mm. and under, majority larval, to 15 mm. and over, majority adolescent. 



Both winter and spring developmental diagrams then are intended to serve a dual purpose, to be 

 read first in conjunction with the winter and spring massed larval distributional charts and later in 

 conjunction with the 1 1-20 mm. (small whale food) distributional charts which follow presently the 

 massed larval series. 



