102 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



a part of the joint, but it does not correspond to the inter segmental groove (cuts 

 13, 14, x) of the cheliped. 



1 have never observed the casting of a claw at any time before the fourth larval 

 stage. Autotomy seems to be occasionally practiced at this period, and in the fifth 

 and following stages it is common. This is illustrated by the history of larva ~No. 

 23, table 34. When this lobster in the fourth stage was placed under observation, July 

 25, it was 13 mm. long and had lost both its large chelipeds and its right fii'th and left 

 fourth pereiopods. When, fifteen days later, August 9, it molted to the fifth stage 

 (length, 15 mm.), the large left cheliped (figs. 92, 96, plate 33) and the fourth and fifth 

 walking legs were regenerated; the right cheliped appeared as a rudimentary stump. 

 Eight days later, August 21, it had molted to the sixth stage (17 mm. long), when its 

 large right cheliped appeared regenerated. The animal was placed in a flat glass dish, 

 and in disturbing it, upon changing the water, it shot off its large left cheliped again 

 and died two days after. 



In the first larva there is a free articulation between the second and third joints of 

 the great chelipeds (fig. 66, plate 30), and there is no true fusion of the segments until 

 after the fifth stage. In the fourth stage the articulation is distinct, as represented 

 in cut 15. This not only shows that the plane of rupture in the large chelipeds 



Cut 15. — Part of first cheliped of fourth larva, showing the base of the limb and distinct articidation 

 between the second and third joints. 

 a-a\ piano of section shown in tig. 169, plate 43; br, podobranehia; x, articulatiou between second and third joints, 

 corresponding to plane of fracture in adult appendage; y, articular process in second joint; 1-4, segments of limb. Drawn 

 from molted shell. 



corresponds to what was formerly a free articulation, but also that this autotomy is a 

 comparatively recent acquisition. It may have been acquired independently in the 

 Macrura and Brachyura. Autotomy of a pronounced character occurs only in limbs 

 where fusion of two neighboring joints has been effected, and was probably produced 

 as a result of natural selection while the fusion was taking place. 



The habit of " casting a claw " being of a purely reflex character, and therefore not 

 subject to the will of the animal, there is needed only the proper stimulus to call it into 

 play. Unintentional experiments in autotomy have often been made by tethering a 

 lobster or crab by its large claws. The animal, of course, escapes, leaving only its 

 members behind. When lobsters are drawn out of the water by the claws, or when a 

 claw is pinched by another lobster, or while they are handled in packing, especially 

 for the winter market, they often "cast a claw;" and the transportation of lobsters 

 at this season is said to be attended with considerable loss in consequence. The old 

 custom of plugging lobsters, which consisted in driving a wooden wedge between the 



