182 



DEPARTMENT OF THE yATAL SERVICE 



The development of Calanus from the egg upwards was followed by C. Grobben 

 in 1881, whose memoir I have not had for reference during the preparation of tliis 

 report. The larval and copepodid stages have recently been described and figured by 

 Marie C. Lebour (1916). All the larval stages are so small that they pass through the 

 fine meshes of the silken tow-net, and this commonly happens with the first two cope- 

 podid stages as well. In order to obtain the earliest stages they must either be reared 

 under laboratory conditions or the finest procurable silk bolting cloth must be used for 

 making the tow-nets. 



It is not knov^rii exactly when the ontogenetic migrations end and the diurnal 

 migrations begin. Esterly (1911) confines his enumerations to stages V and VI which 

 he considered together, rejecting the younger forms. Making allowance for the fact 

 that stage I rarely comes under observation, we may still unite stages I, II, III, and 



IV as a superstage under the term juniores as employed by Gran, in order to compare 

 it with the superstage of which stage V is the adolescent and stage VI the adult form. 

 By grouping certain of the data contained in the tables in the manner indicated, a con- 

 trast appears between the distribution of the juniors and that of the two final stages, 

 the former being more bound up with the surface layers than the latter. For example, 

 at No. S3 station 17 there was a copious and typical microcalanoid plankton of stages II 

 and III, together with Pseudo calanus at the surface (see table VIII). The contrast 

 which is brought out in the subjoined table K is a partial illustration of the ontoge- 

 netic migrations of Calanus finmarchicus. If the closing net could have been used 

 more frequently, and if actual numbers were given instead of percentages, the diffe- 

 rences in the behaviour of the two superstages would have been rendered much more 

 manifest. Of course these ratios have no claim to exactness because so many inter- 

 acting factors disturb the simple relations, but they may serve to bring the problem 

 into relief. 



There is reason to suppose that if stages V and VI were examined separately they 

 might also exhibit differential behaviour. Indications of inverse behaviour of stage 



V and VI (?) are to be found amidst the data recorded in the tables. At Acadia 

 station 39 the surface ratio of V to VI was as 10:40; in the vertical haul from 25-0 

 metres as 15:24; in the vertical haul from 100-0 metres as 26:19. Again at No. 3S 

 station 23, the surface ratio of V to VI was as 0:90; in the vertical haul from 45-0 

 metres as 2:20; in the closing net from 100-60 metres as 5:23; in the closing net from 

 340-145 metres as 15 :2. 



Table K. — Ratio of juniors (II-IV) to adults (V-VI) of C. finmarchicus in surface 

 and vertical hauls. Ac. =^ Acadia; Fs.^= Princess; 7. = Prince; ni = metres; 

 f = fathoms ; jun = juniores ; ad = adolescents and adults. 



