[currie] plankton COPEPODS 213 



many prospective males as prospective females and that, although 

 there is but one average length for stage V, the largest specimens 

 would be famales, since in the adult stage the female averages larger 

 than the male. 



In the 184 specimens of stage V examined, 140 of them had two 

 Se on Ri, only 38 had one Se on Ri, and 6 had one Se on the Ri of one 

 swimming foot (p5) and two on the other. The occurrence of six, out 

 of 184, with one Se on one foot and two on the other is peculiar in that 

 the percentage is too large for them to be classed as mere abnormali- 

 ties. C. finmarchicus V can evidently be divided into three classes 

 as regards the setae on the internal ramus of p5, and these classes do not 

 appear to have any relation to the size of the copepods or to the pros- 

 pective sex of the adult stage. 



Exuviation. It is unknown whether in stage V of C. fiyimarchicus 

 there are certain characteristics which indicate what sex it is to be 

 when it exuviates to stage VI. Microscopic examination of the 

 gonads might throw light on this point. Although copepodite exuvia- 

 tion is continually occurring, yet during ecdysis the vitality of the 

 copepods is so low that they sink towards the bottom of the water. 

 Perhaps this is why it is so rare to find a copepod in the actual process, 

 and it is rarer still to find that the exu\iation has progressed far enough 

 to distinguish, within the exuvia of Stage V, the sex of stage VI. In a 

 few specimens Numbers 1-9, Table II, the commencement of exuvia- 

 tion was only apparent in the eating and swimming appendages and 

 in the caudal furca, especially in p5 where the coxal teeth of stage VI 

 could be seen through the cuticle. Others, numbers 10-18 Table II, 

 were in ecdysis when examined, and the exuviation had progressed to 

 such a degree that the sex could easily be ascertained. These were 

 obtained from Dr. Willey's copepod cultures. 



