164 



Pari III. — Tiventy-first Annual Report 



With the exception of 3a tiie stage of each of these young crabs was 

 known, since they were reared in the Laboratory from the Megalops 

 stage. They are not, however, successive casts of one individual. 



The crab 3a was found on the beach, and from its size it is probably 

 a specimen of the third stage. It cast in confinement, and the resulting 

 form appears in the Table as 4a. 



Food of Megcdops. 



In the ffeces of a Megalops there was a large quantity of diatoms. 



Rate of Growth of Carcinus mamas. 



In the growth of the crab a considerable amount of variation occurs. 

 This is due to the fact that increase in size only occurs after a moult, 

 and the amount of the increase varies not only with the individual, but 

 also in the same specimen in different moults. It is, however, possible 

 with a fair amount of certainty to separate the crabs into year groups, as 

 will be shown later, if attention be given in the case of small crabs to 

 the month in which they are captured. 



In 1884 Brook published a series of observations on the rate of growth 

 of Carcinus. He confined a number of specimens until they passed 

 through a series of moults. He at that time wrote — " It would appear 

 impossible to judge either the age of any particular specimen, or the 

 number of ecdyses which it had passed through, from a casual observa- 

 tion of it on the sea coast, and even in confinement a number of ecdyses 

 must be passed through before any reliable information is obtained." 

 He was of the opinion that two of his specimens which he reared from 

 the Megalops stage, A and B, would have reached the breadth of 35 and 

 56 mm. respectively when two years old. 



For several years Mr. H. J. Waddington, Bournemouth, has devoted 

 attention to the rearing of this form. He has succeeded in obtaining 

 a very complete and valuable series of casts of various specimens. The 

 results of his work he has courteously communicated to me, and with 

 his permission they are incorporated in the present paper. 



They refer to 11 individuals which were kept in confinement for 

 periods varying from 7 to 34 months. The particulars, consisting of 

 the size* of each moult-stage and its date, are given in Table I. The 

 first date and size refer in each case to the size and date of capture. 

 For three Waddington series, viz. Nos. 8, 9, and 10, Table I., I am 

 indebted to Meek's paper on the " Rate of Growth of the Crab."t 

 Alongside the measurement of each cast the ratio of increase is given, 

 and the interval that elapsed between each two moults is appended. 



I have also ai'ranged the data regarding five of Brook's specimens in 

 a like manner in Table II, 



The size consists in the Oreatest Breadth of the Carapace, 

 t Nurthumherland Sea Fisheries Committee. Report on the Scientijii' Investigations for the 

 year 1902. Newcastle-upon-Tyne, 1903, p. 58. 



[Table 



