132 FRANCIS H. HERRICK. 



from the base c. p., Figs, i and 2). As I shall later show how- 

 ever, this twisting of the limb is entirely independent of the form 

 or weight of the claw. Meantime the eight slender legs, which 

 follow the larger pair, have remained stationary, and have retained 

 their larval form and position. 



In the larval lobster the first pair of chelate limbs are pre- 

 hensile organs solely, by which the food is seized and trans- 

 ferred to the mouth-parts. Later, when the double claw is fully 

 developed, and is provided with either crushing tubercles, or 

 rows of interlocked tooth-like spines, the prey is usually crushed 

 and torn in pieces before its delivery at the mouth by the smaller 

 claw-feet. The toothed or " quick " claw is primarily used for 

 striking and capturing the prey. 



The rotation of the chela, in the lobster, is completed at the 

 fourth molt, which marks the most surprising leap in the whole 

 history of development, for at this time the larval swimming 

 organs are laid aside and as Prentiss * has shown, the antennu- 

 lary pockets or balancing organs come into play, when, for the 

 first time the miniature lobster swims steadily, and in an upright 

 position. At this crisis new instincts also arise ; when the lob- 

 sterling swims rapidly at the surface, the great claws are directed 

 forward and held close together, but if its pugnacity is aroused, 

 it assumes the well known attitude of defense displayed by an 

 adult animal. 



In dead lobsters or crayfishes the large claws, in response to 

 gravity, lie perfectly flat, but this position cannot be assumed in 

 life unless the muscles of the limb are completely relaxed. In 

 the common-position of wariness and defense, the claws are up- 

 raised, and tilted obliquely inwards, so that their tips rest close 

 together on the bottom. 



In both Cambarus and Homarns the disposition of pigment is 

 a more striking index of the rotation of the limb than changes in 

 its form, and even more than in the crab have the under sides or 

 what were once the anterior faces of the claws become differen- 

 tiated by the absence of color. The mottled green pigments 

 which are so thickly spread over the whole upper surface of these 

 animals are completely lacking on the under sides of the big claws. 



* "The Otocyst of Decapod Crustacea : Its Structure, Functions, and Develop- 

 ment," Bull. Mus. Comp. Zoo!., Vol. XXXVI., 1901. 



