of the Fishery Board for Scotland. 



173 



female, 43-7. The inclusion of the other males and females just noted 

 reduces the averages to — Males 51*1 mm., and females 39 '3 mm. 



Three crabs (Nos. 3, 10, and 11) lived to complete their third year. 

 They measured respectively — Male 59*5, female 55 : 55. The crab No. 

 17, which was 62 mm, broad in its second year, did not cast again 

 during the succeeding twenty months ; it died soon after that interval. 

 60 mm. may be taken as the size of the three-year-old male and 55 

 for the three-year-old female. 



The conclusions regarding the rate of growth of the crabs under 

 discussion are as follows : — 



1 Year, 8-22 mm. Average 13*5 mm. 



2 Years, { 5 35:48.n„. Average { 



•{ 



6 51 mm. 

 $ 39 mm. 



3 Years, ^ ^ 



' o5 mm. 



Meek estimates the rate of growth as follows : — 



One year, average 9 mm. : two years, average 37 mm. : three years, 

 average 55 mm. : four years, average 69 mm. 



The discussion has rested principally on Waddington's series, and of 

 these the specimens which were got at a very early stage are especially 

 valuable. The larger crabs which were introduced into the second year 

 division had, by their subsequent growth, apparently justified the 



arrangement followed. 



The number of specimens under consideration is small, and it is 

 difficult to know how far the conclusion may be legitimately applied 

 directly to the crab in nature. A considerable amount of variation was 

 shown in the growth of the crabs in their first year, and this it may be 

 taken for granted occurs in nature, possibly to as great a degi-ee as in 

 the confined crabs. In the second year there was a tendency to eliminate 

 the differences, a hastening of the development in the backward 

 specimens up to the level of the more forward individuals. 



It appears very probable that the results will agree on the whole very 

 closely with the life of the crab in the free state. 



Moulting — The Eatio of Increase. 



The number of moults through which a crab passes in a year appears 

 fairly constant. Thus during the first year they were 8 to 11 in 

 number; in two years, 14 to 17; and in three years 16-18. That 

 moulting does not depend on the supply of food alone is apparent from 

 the fact that the ratio of increase is so variable, vide Tables I. and II. 

 The ratio of increase, that is the actual increase (mm.) at a moult, divided 

 by the previous size of the crab, varies from y^- to f : it is very often 

 about |. In the earliest stages the moults follow one another rapidly, 

 sometimes two {e.g. Nos. 7, 18, 19) or even three (No. 20) occurring 

 within a month. The rate of growth decreases with age (Meek). The 

 Tables do not show a regular decrease in the ratio, but the decrease in 

 the rate of growth is (sfiected by the less frequent moulting or its cessation 

 altogether. 



Early Spawning. 



Two females, Nos. 3 and 10, extruded their eggs in winter before the 

 end of their third year. One of them extruded its eggs the previous 



