210 THE ROYAL SOCIETY OF CANADA 



there are two averages, one large and the other small. The occurrence 

 of these two size-classes gave rise to the supposition that there might 

 be an ecdysis intercalated within this stage. Of twenty-seven 

 examples examined from a vertical haul made on May 24th the averages 

 were 2 • 5 mm. and 3 • 2 mm. ; of 116 examples from a 10 fathom tow on 

 June 28th, the averages were 2- 1 mm. and 3- 1 mm. Both in the haul 

 and in the tow there were a great many more of the smaller individuals, 

 23 of the 27 from the vertical haul and 87 of the 116 from the tow, 

 belonging to the small size class. If there were an exuviation during 

 this stage such a large variation in the numbers of the individuals of 

 the two sizes would not be expected, but if there were two races of 

 C. finmarchicus, this variation could be easily explained by one race 

 being more numerous than the other. 



The coxal teeth of the fifth feet in stage IV, besides varying in 

 number, seem to have no regularity in their distribution. Usually 

 they are more or less scattered, although sometimes, on one or both 

 of the feet, they may be in a distinct transverse or marginal row, or 

 they may be in a row and scattered as well. They are arranged in 

 two principal ways, which correspond to the two leading size classes, 

 as is shown by the similarity of the graphs 1 and 2. 



In the one class, containing small individuals, the teeth 'are 

 generally few in number, from three to ten, and of a certain size, 

 but they may be more numerous and smaller, the numerical and 

 substantive variation in this regard showing no regularity. In the 

 other class containing large individuals, generally there are from 

 eleven to eighteen teeth of a large size. Graph 3 shows the correla- 

 tion between the lengths and the teeth. As a general rule, the shorter 

 the individual the fewer are the coxal teeth. The few-teeth-small- 

 size-class includes those with lengths from 1-8 mm. to 2-7 mm., and 

 teeth from three to eleven in number. The many-teeth-large-size- 

 class includes those with lengths from 2-7 mm. to 3-2 mm. and teeth 

 from eleven to eighteen in number. Since one class contains many 

 more individuals than the other, one might be led to believe that the 

 supposition that there are two races of C. finmarchicus is correct, 

 though not definitely recognizable in later stages. 



Although in both these classes there is no regularity in the dis- 

 tribution of the coxal teeth, yet each has a characteristic appearance. 

 A typical example of the teeth of the small size is given in Fig. 6, and 

 of the large size class in Fig. 18. The small size class may have large 

 or small teeth. As a general rule when the teeth are large they are 

 not so numerous as when they are small. Some specimens occurred 

 with comparatively large and few teeth (Figs. 8, 11), while others had 

 small and many teeth (Figs. 9, 10, 12) ; and there were quite a number 



