CAyADIAX FISHERIES EXPEDITION, 191. ',-15 



183 



PART II. 



NOTES ON SPECIES. 



1. Calanus finmarchicus. — There is a wide range of variation in the size of the 

 individuals during the several copepodid stages and this is often to be observed at one 

 and the same station. It is assumed that the transition from one stage- to another is 

 effected by a single exuviation. In one case I observed the new cuticle of stage V 

 forming beneath the old cuticle of stage IV, as shown most clearly by the coxal denti- 

 culation of the fifth foot. The denticulation on the inner margin of the basal joint 

 of the fifth foot occupies the whole of that margin in both stages V and VI; at stage 

 IV only the middle third of the coxal joint shows the marginal denticulation (text fig. 

 I). It is to be noted that the outer denticulation shown in the figure is much more 

 restricted in certain individuals. 



Fie 



1. — C. fimiuirchicus stage IV, length 32 mm.; fifth feet showing 

 transition to succeeding stage. Acadia station 9. 



By employing biometrical methods. Gran (190.) found that within the limits of 

 the Norwegian North Sea, the individuals averaged larger in the north than in the 

 south. For example at stage III (synonymous with Gran's fourth stage) the maximum 

 length of the forebody in individuals captured in latitude 60° 43' N. was 1-25 mm., 

 while in those taken in latitude 67° 41' N. the maximum length of forebody was 1-4S 

 mm. Gran also found in general that the stages are smaller in summer than in spring. 

 It is doubtful whether these biometrical results are applicable to other regions. To 

 render the history complete, it would be necessary to take stock of the frequency of 

 exuviations, and up to the present this has not been found practicable. 



