of the Fishery Board for Scotland. 



Ill 



In the majority of cases the ratio of increase is -Jto J of the original 

 size. In Nos. 3 and 4 the ratios were ^ and \. These crabs were, how- 

 ever, measured immediately on casting, and while the skin was still pliable 

 and nutty-like. In the cases of Nos. 1 and 2 the shell had hardened suffici- 

 ently to be quite firm and resistant at the time it was measured. From 

 the published descriptions of the remaining crabs, with the exception 

 of Couch's specimens, I gather that they were measured some time 

 after casting, when the shell had hardened more or less. Herrick* 

 found, in the lobster which he observed cast its shell, that the size shortly 

 after the moult was 12 inches, while four days afterwards it measured 

 a little short of 12^ inches. So far, then, it seems probable that the 

 increase in size after casting takes place not merely immediately after 

 the escape from the shell, but also during hardening. Until further 

 observations have been made upon this point, the average ratio cannot 

 be known. This question has a direct and important bearing upon the 

 rate of growth of the crab. While, without doubt, considerable varia- 

 tion will be found in the increase, the cases given in the above Table, 

 with four exceptions, point to the ratio of increase being about | to \ of 

 the original size. 



Regeneration op Limbs — Repair of Injuries. 



One of the features of the life -history of crustaceans which has 

 attracted much attention is the renewal of limbs which have been acci- 

 dentally lost. This process is intimately associated with the activity of 

 the dermis, which results in the renewal of the whole skeleton when it 

 has been discarded on casting. From evidence afforded by the examin- 

 ation of the small edible crabs, which are found between tide-marks, I 

 am led to the conclusion that the regeneration of the appendages only 

 takes place when the crab is preparing to cast. This view, although not 

 expressly stated, is more or less borne out by previous investigators ; it 

 is in part suggested in the case of the larval lobster by Herrick. Thus, 

 Reaumurf said that the new limbs of the crayfish " grow more or less 

 rapidly, like plants, according as the season is more or less favourable ; 

 the warmer days are those which hasten the more their formation and 

 growth. Sometimes new legs sprout out in three weeks, sometimes 

 not till after six ; and when the legs are broken off in winter, they do 

 not grow again till summer." Chantranj found in the crayfish that 

 " in the first year of life 70 days are necessary for the regeneration of 

 new limbs. The adult female requires three to four years, the male 

 one and a half to two years, to repair its limbs ; and we are told that 

 the adult male moults twice and the female but once a year." . 

 " The eyes of the crayfish when cut off in October, at the end of the 

 season of moulting, are not regenerated until the following May, when 

 a series of moults begin." HerrickJ says that in the 4th and 5th larval 

 stages of the lobster — "at the moment the limb is broken off blood 

 immediately oozes out and coagulates, forming a dense crust over the 

 stump. In a short time a small white papilla, which represents the 

 rudiment of the new limb, appears in the midst of the brewn hardened 

 clot. The papilla continues to grow independently of the moulting 

 process, though covered with a cuticular membrane, until a miniature 

 appendage is formed." " The time required for the renewal of a 

 limb thus depends upon the time at which an injury occurs with 

 reference to the moult, and also upon the physiological condition of the 



* Op. tit., p. 85. 



f From Herrick's Monograph on the American Lobster, pp. 103, 104. 

 % Op. cit., pp. 104, 105. 



