100 Part III, — Twenty-second Annual Report 



II.— CONTRIBUTIONS TO THE LIFE-HISTORIES OF THE 

 EDIBLE CRAB {CANCER PAGURUS) AND OF OTHER 

 DECAPOD CRUSTACEA : -IMPREGNATION : SPAWN- 

 ING : CASTING : DISTRIBUTION : RATE OF GROWTH. 

 By H. Chas. Williamson, M.A., D.Sc, Marine Laboratory, 

 Aberdeen. (Plates I.-V.) 



CONTENTS. 



TAGE 



The Impregnation of Cancer pagurus, . . . 101 



The Muscular System of the Abdomen of the Male 



Crab, . . . . . . 103 



The Action of the Penis, . . . . 104 



The Condition of the Spermatheca, . . . 105 



The Impregnation of Carcinus mcenas, . . . 107 



The Spawning of Cancer pagurus, .... 108 



The Mode of Attachment of the Eggs to the 



Swimmeret, ... . . . 108 



The Swimmeret, . . . . . 110 



The Endopodite, . . . . . 110 



The Exopodite, . . . . . Ill 



The Ripe Egg, . . . . . 112 



The Attachment of the Eggs, . . . 115 



The Sloughing of the Empty Egg-capsules, . . 1J6 



The Attachment of the Eggs in other Decapod Crustacea, 116 



The Spawning of Carcinus mamas, . . . . 120 



The Casting, Distribution, and Rate of Growth of Cancer 



pagurus, . . . . . . 121 



The Migrations of Cancer pagurus, . . . . 135 



The Changes in the Carapace of Cancer pagurus, . . 136 



Literature, . . . . . . . 137 



Explanation of the Plates, . . . . . 1 38 



In tbe Eighteenth Annual Report of the Fishery Board (1900) I 

 published a paper dealing generally with the life-history of the crab. 

 Since then I have, as occasion offered, continued my observations on this 

 form, and on other Decapod Crustacea. Attention has been directed 

 specially to the phenomena of Impregnation and Spawning. AVhile the 

 fact of the impregnation was well evidenced by the presence of the 

 internal spermatheca liberally stocked with sperms, the exact mode in 

 which the sperms were transferred to the female was not very apparent. 

 With a view to elucidating the process a detailed examination has been 

 made of the copulatory organs of the male, and the spermatheca of the 

 female. While every stage in the process of impregnation has not yet 

 been determined, still a considerable advance towards the full description 

 of it has been attained. 



In connection with the spawning of the higher Crustacea the attach- 

 ment of the eggs to the endopodite branches of the pleopods has been 

 variously described. The secret of the attachment has been ascribed to 

 various agencies, the principal of which has been the assistance of a 

 strong cement which glued the eggs to the hairs. This I have been able 

 to show is not the case. The stalk of the egg is really formed by the 



* " Contributions to the Life-History of the Edible Crab {Cancer pagurus)." Eighteenth 

 Annual Report of the Fishery Board, Part III. 



