of the Fishery Board for Scotland. 



109 



says that "a lobster is not completely hard for seven or eight weeks 

 after moulting." A lobster which cast its shell in the tanks at Culler- 

 coats Laboratory during the night 17th- 18th August " was found " by 

 Meek* "to be apparently quite hard on 26th August; so that the 

 hardening appears to be a relatively quick process in the lobster." One 

 of the lobsters confined in a floating box by Cunninghamt cast on 

 November 23rd, and was found to be hard on February 9th. 



Frequency of Casting. 



In its earliest stages there is reason, from the analogous case of the 

 lobster, for believing that the young crab moults more than once a year, 

 but in the stage immediately preceding the adult condition, from 3 to 4 

 inches in breadth, it probably casts only once a year. The shells of 

 these crabs are on the whole clean, and have few ectozoa attached to 

 them. The latter are always small ; the commonest being Serpula, 

 Spirorbis, and Anomia. Certain of these crabs, which have been referred 

 to above (p. 84), and which gave evidence of not having cast during the 

 preceding year, were found to be apparently in a diseased condition. 

 It is very probable, indeed, that the great majority do cast once a year. 

 A considerable number (525) of crabs measuring 3 to 4-J inches were 

 labelled and set free in December, January, February, March, April, 

 May, June, and July, and of these very few were recovered. This may in 

 a great measure be due to the fact that, owing to their annual 

 shedding, they got rid of the labels in summer. Of the 16 which were 

 recaptured, two were obtained in July, one in August, and one in Septem- 

 ber. None were obtained later in the year than September, that is to 

 say after the casting period. The crab captured in August, although it 

 was hard when set free, was then brittle and was evidently preparing 

 to cast. 



The mature crabs above i\ inches in breadth, there is abundant 

 evidence to show, do not cast every year. Certain female crabs 

 measuring from 4J to 5f inches which are unfertilised may, however, 

 do so. The shells of the adults are found covered with a varied 

 collection of ectozoa — viz., Balanus, Serpula, Anomia, Membranipora, 

 zoophytes. I have also on two occasions found, in cases of injury to 

 the gill chamber, mussels and Saxicava attached to the gills. Large 

 oysters have been found attached to the backs of crabs. The size of 

 these molluscs in certain cases proves that the crabs, their hosts, had 

 not cast for three and four years. Buckland % mentions two large 

 crabs, a male 6| and a female 7J inches, which had on their backs 

 oysters 3 inches across. The crabs could not have cast for three 

 years. In the Fish Trades Gazette for December 9th, 1899, a crab 

 was recorded upon which was fastened a four-year-old oyster. It is 

 now in Ipswich Museum. While from the fact that the female crab 

 usually carries two lots of eggs in successive years we know that the 

 female does not probably cast oftener than once in two years, we have 

 here collateral evidence indicating even a longer abstention from casting. 

 From an examination of the labelled crabs which were put away when 

 soft, it is seen that certain of the ectozoa, zoophytes especially, attach 

 themselves to the crab earlier in the year than October. All the soft 

 crabs which had been set free up to and including the month of Septem- 

 ber, when recaptured had large growths of zoophytes, and also showed 

 Anomia and Serpula ; whereas the soft crabs of October were almost 



* Op. cit., p. 54. 

 f Op. cit., p. 41. 

 X Op. cit., p. 11, 



