NATURAIy HISTORY OF AMERICAN LOBSTER. 257 



food, and to emphasize the function, we shall call it the cracker, crusher, or crushing 

 claw; the smaller and slenderer, which suggests a patent lock forceps with serrated jaws, 

 is used for seizing, holding, piercing, tearing, and slashing the prey. We shall call it 

 the lock forceps or toothed claw, in preference to the phrase "cutting claw" formerly 

 used. In young animals from 2 to 5 inches long the teeth of this weapon are completely 

 concealed by dense clusters of sensory hairs, which though seldom absent become less 

 conspicuous with advancing age. It is therefore evident that the toothed claw is highly 

 sensitive and "feels" the blows it gives as well as those it takes. 



Przibram (223), who classifies the higher Crustacea according to the similarity or 

 differentiation of the big claws into the " Homoiochelie," and the " HeterocheUe," calls 

 the larger claw the "Knoten" or " Knackschere," and the smaller the "Zahnchen" or 

 "Zwickschere," in view of their form and function respectively. Stahr {2^7), who uses 

 the terms " Zahnchenschere " (toothed claw), and " Knotenschere " (knobbed claw), as 

 descriptive of their structure, after a discussion of their probable functions, says that he 

 is justified in designating the claws of Homarus gammarus as follows, "the beautiful, 

 regular, elegantly formed, thin-walled forceps, provided with periodic teeth and sensory 

 hairs as the ornamental ("Schmupk-") and sensory claw ("Spiirschere"), and the other, 

 plump, oval, thick-walled form, provided with tubercles, as the crushing (" Knack-") and 

 grasping claw ("Greifschere"). As will later appear, the development of these organs 

 affords no warrant for regarding the toothed claw as an ornament, not to speak of the 

 psychological difiiculties involved. 



TORSION OF THE LIMB. 



Of greater interest than the difference in size and structure of the big claws is the 

 complete change in their position on either side which takes place after birth, due to a 

 twisting of ^the limb and mainly of the fifth joint or carpus or the third podomere reck- 

 oned from the distal end. 



This curious torsion of the crustacean leg is of very ancient origin, dating from as 

 early as the Cretaceous period, and is shared by many of the higher Crustacea decapods 

 (for first account of torsion and fuller discussion see 153). It further affords a good 

 illustration of how a very obvious fact may long escape the notice of naturalists, my 

 own attention not having called to it until 1905, although drawings of the larval and 

 adult stages had been repeatedly made. 



In the adult lobster or crayfish the free dactyls of the smaller chelate legs aU open 

 upward and outward in a plane which is nearly vertical, while in the big claws the 

 dactyls of opposite sides face and open inward or in a nearly horizontal plane. In the 

 lobster at birth, on the other hand, and up to the fourth stage, aU the chelae have the 

 same relative positions; all open vertically upward with an outward inclination. (Com- 

 pare fig. I, 6, and 7 with pi. xxviii.) 



It is thus evident that the position of the great forceps in an adult animal has been 

 reversed through a rotation of either claw through an angle of 90°, toward the median 

 plane of the body, in consequence of which their iimer or anterior faces have become 



