of the Fishery Board for Scotland. 



L05 



water." The body fluid of the crab is not water; it is richly albuminous. 

 On exposure to air for a little time it becomes black ; and if a quantity 

 of it is treated with picro-sulphuric acid it coagulates into a solid mass. 

 A soft crab is characteristically coloured ; the dorsum is a light brick 

 red, the under-surface (epimera) is white ; the dorsal surface of the 

 great claws is red, the under-surface white. In a hard crab the white 

 portions have a creamy or yellow colour. A crab remains " soft," 

 legally, as long as it is possible to push the thumb through the shell in 

 the gill region or near the great claws ; this it is still possible to do three 

 months after the time when the crab casts. When it is quite hard 

 through increase in thickness and calcification of the shell, four 

 months after casting, the general appearance of the crab has changed a 

 little ; the white portions have taken on a slight creamy colour, but 

 otherwise the colours are bright and the shell clean. The crab is then 

 known as a " china crab." 



A crab which is not uncommon at Dunbar in autumn and winter, 

 but found only during these seasons, is known as a" milker." It is to 

 all appearance a hard crab ; the white portions of the shell and claws 

 have taken on a distinct cream colour. On testing it, however, the shell 

 is found to be thin and brittle. There is a considerable amount of body 

 fluid, but this, in contradistinction to the colourless body fluid of the 

 normal soft crab, is white like milk. On treatment with picro-sulphuric 

 acid it does not coagulate into a solid mass, but settles down as a 

 somewhat flocculent precipitate. Microscopic examination reveals great 

 numbers of small bodies which are probably the same micrococci 

 described by Cuenot* as having been found in Carcinus mamas. The 

 crab itself is usually small, and the hardening process has been checked 

 by these parasites. 



The Occurrence of Soft Crabs. 



As to the time of the year when casting takes place, while there is 

 evidence that the principal time of casting is from July to September 

 (both inclusive), still, from the occurrence of soft crabs, it is to be 

 inferred that casting takes place during a large portion of the year, 

 viz. from May to November inclusive. I have records of adult soft crabs 

 for every month of the year except April. In Table V., p. 102, are given 

 statistics of catches of crabs during each month of 1899. In addition 

 to these, I received in May two female soft crabs measuring 4| by 6| 

 inches ; and in June Mr. Hutchison, Dunbar, observed a large soft 

 male ; in March he noted a soft crab 5| inches across, Cunninghamt 

 records a crab which cast in April. In the case of the small beach 

 crabs —the statistics of which (Table IV., p. 101) were kept by myself — 

 some were found soft in each month of the year except April and May. 

 One soft crab alone was found in February, and it had just cast. 

 It would then appear that casting is not confined to the summer 

 months ; but the crabs which cast at other times of the year are pro- 

 bably a very small minority. The largest number of soft crabs is seen 

 to occur in the months August to November inclusive. The statistics 

 for October are deficient. It is not known how long a small crab 

 remains soft, but, judging from the time which is known to elapse 

 before hardening is completed in the adult crab, it is probably not less 

 than two and a half months. It is also possible that a crab which casts 

 late in the year will take longer to harden than those which cast early, 

 say July. A large number of those found soft in November, then, might 



* Cuenot, "Etudes physiologiques sur les Crustace's Decapodes." Archives deBiologle, 

 T. XIII, , 1895. 

 f Op. cit, p. 42. 



