THE MODERN LIMULUS DESCRIBED. 211 



Venus mercenaria ; the siphons were instantly withdrawn, and the less agile King-crab 

 found himself next moment a prisoner with his limb nipped firmly between the valves of 

 the outraged Venus. But here an important difference is noticeable between Limulus 

 and an ordinary Crab or Lobster ; had either of these been thus trapped by the leg, they 

 would have speedily made good their escape by giving their body a violent jerk and 

 leaving the imprisoned limb behind them, a cicatrix forming over the articulation for the 

 lost limb, which after three or four moults would not only have been reproduced, but 

 would have regained its normal size. It must, however, be borne in mind that the leg 

 of a Decapod is not homologous with that of Limulus, whose organs of locomotion are 

 modified palpi or maxillipeds rather than true feet, all its walking-appendages being 

 mouth-organs at their proximal end, which would render their replacement in Limulus 

 as difficult as would be that of the maxillae or maxillipeds in a Decapod Crustacean, of 

 the separate reparation of which we have no recorded instances. 



The periodic exuviation of Limulus seems to be a very simple and expeditious 

 process. " A thin narrow rim runs round the under side of the anterior portion of the 

 cephalic shield. This is in fact the widest part of the animal. Just before the time for 

 exuviating a separation occurs between this rim and the perimeter of the anterior 

 shield. To the unaided eye this rent is altogether imperceptible, but it splits open on the 

 exertions of the animal; and at this opening it emerges from its old shell. As the 

 opening is in front and in the place of greatest width, and moreover as the shell is 

 subcoriaceous and somewhat yielding, and at this particular place is very thin, Limulus 

 enjoys in this respect a great advantage over the higher Crustacea, whose moult takes 

 place by a separation between the posterior border of the carapace and the abdomen, and 

 whose shell is composed of more unyielding materials. 1 



" The exuviation of the King-crab takes place several times during the first year, 

 and at very short intervals. How many I do not know, as that must vary according to 

 the time of hatching. But I think," says Dr. Lockwood, " the young produced in the 

 latter part of June will accomplish five or six moults before the cold weather comes " 

 (op. cit., p. 261). 



The same author records the exuviation of a large female Limulus, which measured 

 eight inches in the shorter diameter of its cephalic shield, but which after moulting was 

 nine and a half inches when measured in the same direction. He justly observes, " if 

 they moult more than once in the year, this would make their growth rapid ; and if they 

 do not, they must attain an age of not less than eight years before reaching the size that 

 indicates adult life." 



The same excellent naturalist observes, " every spring, as soon as the water has lost 

 its winter temperature, large numbers of the young of the previous summer are found in 

 the shallows. These range from an inch to two and a half inches in the shorter diameter. 

 As the creature, when beginning life for itself, is scarcely a quarter of an inch in diameter, 



1 Op. cit., p. 257. 



