30 



state, and time must elapse before they are ready for extrusion. 

 The period of incubation does not appear to be a long one, but 

 as I stated in 1902, it is not likely shorter than four months. 

 It is probable therefore that a year is taken up at least in these 

 processes, that, in other words, the next ecdysis after that in 

 which pairing occurs for the first time will be at the end of a 

 year. It will be noted, however, that at about the period of 

 the twenty-first ecdysis a long interval is bound to occur, for 

 growth would not warrant an earlier ecdysis. These and other 

 correlated points will gain in clearness by a consideration of the 

 growth of the edible crab. 



We do not yet possess full information as to the larval history 

 of the edible crab, Cancer pagurus, but so far as we know it appears 

 to be precisely similar to that of the shore crab. The protozoeae 

 have seven pairs of functional appendages, and the pelagic stages 

 which lead to the megalopa are completed in about a month or a 

 little more. The megalopa gives place to the first young stages, 

 and we have to thank Cunningham for drawing attention to their 

 remarkable likeness to Atelecyclus. The evidence upon which 

 an estimate of the growth is based was presented by Williamson 

 in 1904 and by me in 1905. It consists of three series of stages 

 reared by Mr. H. J. Waddington at Bournemouth, two of which 

 refer to females, the third with the sex not determined, William- 

 son's careful records of the crabs collected in the region of Dunbar, 

 and the observations made at Cullercoats. 



From the Waddington series we can see that a female may 

 attam a size of 30-35 mm. in a year after hatching, and 46-56-5 mm. 

 in two years. From Williamson's measurements of the crabs 

 of the beach at Dunbar (fig. 7) it may be seen that during the 

 summer, from May to July,, crabs of about 20 mm. appear between 

 tide marks, that they reach a size of about 30 mm. in August and 

 September, and 40 mm. in October and November. We see some 

 evidence also that the larger of these leave the inshore during 

 the succeeding winter months, reappearing, however, to some 

 extent in the spring and summer. 



Taking these observations together we have the means of 

 fixing the general growth during the first two years, and we can 

 see also that there is a wide range of variation. The later stages 



