Mr Mcintosh, On Variation in the Norway Lobster. 443 



2. As to the proportion of the sexes. 



The difference in the relative proportion of male and female 

 lobsters in the Forth and Clyde areas is even more noteworthy. 

 For example, Mr Marshall found only 68 females (that is, 6"4 per 

 cent.) in a total of 1068 specimens, and he naturally comments 

 on the relative scarcity of these. Among the Clyde lobsters, on 

 the other hand, no fewer than 51 4 per cent, of the specimens 

 examined were females. The difficulty of explaining the difference 

 is rather increased than otherwise by Mr Marshall's statement 

 that of the 80 specimens caught off the Isle of Man only two 

 were females. It would thus appear that the Isle of Man 

 specimens resembled those from the Firth of Clyde in regard to 

 the number with abnormal genital apertures, while markedly 

 differing in the proportion of the sexes. 



The Clyde specimens were absolutely unselected, for account 

 was taken of every specimen which the dredge brought up. It 

 is difficult to discover to what extent, if any, Mr Marshall's 

 specimens were selected, since they were obtained from the fish- 

 market at Newhaven (at various times during the spring, summer 

 and autumn of 1901). In view of the fact that females are on 

 the average considerably smaller than males, it is not improbable 

 that a proportion of the females, being smaller, was not landed. 

 For example, I found that the average length of the 656 specimens 

 examined was 110 mm. The average length of the females was 

 102 - 4 mm. and the average length of the males was 1182 mm. 

 This same fact is illustrated in another way in Table III, where 

 are summarized the results of measurement of the length of 

 body of males and females. (The measurement was made from 

 tip of rostrum to end of telson, and it was noted that the length 

 of carapace measured along the dorsal line is almost exactly half 

 that of the abdomen.) An examination of this Table seems to 

 justify the conclusion that on the whole the male is larger than 

 the female. 



Table III. 



