110 



Part III. — Eighteenth Annual Report 



devoid of ectozoa; occasionally a small zoophyte was discovered. One 

 crab which was soft in November was found in the following May 

 to have on its dorsum an Anomia J-inch (6*5mm.) across, and a Serpula 

 f-inch (11mm.) long. 



The labelling experiments afford some evidence with regard to the 

 frequency of casting of the mature male. Thirty five large hard 

 crabs (male and female) were labelled in J une and July 1899. They were 

 set free at the mouth of the harbour, Dunbar. Of the J une specimens, 

 four males were recovered — viz., one in July, close to the harbour ; one in 

 September, 2 miles N.E. from Dunbar in 22 fathoms ; two in October, 

 2 miles N.E., 22 fathoms, and 1| miles E. by S., 18 fathoms, respectively. 

 One of the July lot, a male, was got in December 3 miles N.E. 

 of Dunbar. These crabs then shew that the large male crabs also 

 do not cast oftener than once in two years. As a rule, the shell of the 

 old female crab is much more dirty than that of the male. The white parts 

 of the shell of the male turn a deep amber colour, but it remains on the 

 whole very free from mud. The female, however, probably from its 

 habit, when carrying eggs, of lying half-buried in the mud, becomes 

 very dirty, the hairs on the epimera, the fringes of the abdomen, and 

 the exopodites of the swimmerets being often quite black. 



Increase in Size on Casting . 



So far the law of growth of the crab has not been investigated, and 

 for the determination of the increase which takes place at certain sizes 

 we are dependent on a few recorded cases. These are set out in the 

 following Table : — 





Original 

 Size in 

 Inches, 



Size of 

 Soft Crab. 



Increase. 

 Inch. 



Ratio of 

 Increase. 



1 



Authoiity. 



1 



2 



£ 



1 3 



1 



If 



l 



5 



3 

 8 



I 



3Ti 



Mar. Lab.. 

 Dunbar. 



3 



9 1 



Z T6 





I 





5> 



4 



24 





A 





J I 



5 



2| 



H 



7 



8 





J. Couch. 



6 







9 

 TO 







7 





5 







Buckland. 



8 



4 









Gatty Lab., 

 St Andrews. 



9 



in 





» 





Wilson. 



10 



H 



H 



if 





Meek. 



11 



H 





3 

 4 





J. Couch. 



12 



n 



1 





H 





Cunningham. 



