212 TPIE ROYAL SOCIETY OF CANADA 



Stage V. At this stage there are five free thoracic segments in 

 the forebody and four segments in the urosome. The antennae, 

 mandibles, maxillae, anterior maxilliped and four pairs of swimming 

 feet are like the adult. The posterior maxilliped has not the full 

 number of setae and the last swimming foot (p5), although it has the 

 full number of setae, has only two segments in each ramus. 



Length variation. Upwards of two hundred specimens were 

 measured and the coxal teeth counted. The total length from the 

 front of the head to the end of the caudal rami varied from 2-5 mm. 

 to 4-68 mm., the average being 3-2 mm. Although there was such a 

 variation in length, yet there were no abrupt changes as in stage IV. 

 There is the one average of 3 • 2 mm. about which the lengths fluctuate. 

 If there had been two races of C. finmarchicus, as our observations of 

 stage IV seemed to indicate, we would have expected to find them 

 represented in stage V. 



Coxal teeth. The denticulations on p5 at stage V are arranged 

 like those of the adult in a regular row, usually with a slight sigmoid 

 bend in the middle of the row, along the inner margin of BI. The 

 number of teeth varies from twenty-four to forty-four, the average 

 being thirty-two. The right Bl has rarely the same number of teeth 

 as the left, but there is no regularity in this variation. Occasionally 

 a specimen will be found with many more teeth on one side than on 

 the other. When this is the case, the teeth that are more numerous 

 are correspondingly sm.aller in size. One individual had exception- 

 ally few large teeth: eighteen on the right, ten on the left (Fig. 23). 

 This variation from the average number and size of the teeth is so 

 great, that it may be classed as an abnormality. Very often, in 

 addition to the long regular row of teeth, there are a few supernum- 

 erary teeth either at the proximal end of the series or at the distal end. 

 The number of teeth at this stage makes no difference in the number 

 of teeth in the succeeding stage VI, as the teeth of stage VI are formed 

 quite independently of those of stage V. (Figs. 24, 25). 



Setœ. In the Account of the Crustacea of Norway, (Vol. IV, 

 Calanoida I and II, Plates II and III) G. O. Sars figures the p5 of C. 

 finmarchicus female with one external seta on the Ri and that of the 

 male with two external setae (se) on the inner ramus. Marie Lebour 

 (op. cit.) describes stage V as having "swimming feet like adult except 

 the fifth pair which has the full number of bristles, but only two 

 segments to the endopodite and exopodite." If this were the case it 

 would be expected that the copepods of stage V destined to be females 

 would have one Se on Ri of p. 5, and that those destined to be males 

 .would have two Se on Ri. According to the general law of nature 

 we would also be justified in expecting that there would be just as 



