Section IV, 1918 [207] Trans. R.S.C. 



Exuviation and Variation of Plankton Copepods with special reference 

 to Calanus finmarchicus. 



By Mary E. Currie, B.A., McGill University. 



Presented by J. P. McMurrich, Ph.D., F.R.S.C. 



(Read May Meeting, 1918) 



In the life history of Calanus finmarchicus it has been observed 

 that twelve stages intervene between the laying of the egg and the 

 attainment of maturity. The first six of these are the nauplius or 

 larval stages; the others are the copepodite or postlarval stages. 

 Successive stages are separated from one another by an exuviation 

 and, contrary to what occurs among higher Crustacea, the copepods 

 undergo no further exuviation after sexual maturity has been reached. 

 All copepod exuviations are, therefore, developmental and not merely 

 the result of continuous growth. 



The changes in external form which Calanus undergoes in passing 

 from one stage to the next have been described recently by Marie 

 Lebour ("Stages in the Life History of Calanus finmarchicus," Journ. 

 Mar. Biol. Ass. Plymouth, XI, March, 1916), whose paper is not 

 concerned with questions of variation in growth and consequently 

 does not anticipate the results contained in the present report. In 

 his "Notes biologiques sur les Copepodes de la mer Norvégienne" 

 (C.P. I.E.M. Pub. Cire. 22, Copenhagen 1905) D. Damas defined the 

 copepodite stages of C. finmarchicus and stated that the five phases of 

 metamorphosis leading up to the adult form probably correspond to 

 as many successive exuviations. The extraordinary variation in 

 length met with in stage IV., together with the character of the coxal 

 teeth or denticulations on the inner margin of the basal joint of the 

 fifth pair of swimming feet, to which neither Marie Lebour nor D. 

 Damas makes any reference, might lead to the supposition that an 

 additional moult would be intercalated within the period occupied by 

 this stage, but this is not so. There remains the possibility which 

 can only be substantiated by experimental rearing, that there is more 

 than one race of C. finmarchicus in the material examined. The 

 stages which were studied at the Atlantic Biological Station, St. 

 Andrews, N.B., during the months of June, July and early part of 

 August 1916, were III, IV, V, and VI., the last including the adult 

 male and female. Besides C. finmarchicus, observations were made 



