278 THE RATE OF GROWTH [ch. 



ticularly well developed in arthropod animals, and is sometimes 

 accompanied by remarkable modification of the form of the 

 regenerated limb. A case in point, which has attracted much 

 attention, occurs in connection with the claws of certain Crustacea*. 



In many of these we have an asymmetry of the great claws, 

 one being larger than the other and also more or less different in 

 form. For instance in the common lobster, one claw, the larger 

 of the two, is provided with a few great "crushing" teeth, while 

 the smaller claw has more numerous teeth, small and serrated. 

 Though Aristotle thought otherwise, it appears that the crushing- 

 claw may be on the right' or left side, indifferently ; whether it be 

 on one or the other is a matter of "chance." It is otherwise in 

 many other Crustacea, where the larger and more powerful claw is 

 always left or right, as the case may be, according to the species: 

 where, in other words, the "probability" of the large or the small 

 claw being left or being right is tantamount to certainty f. 



As we have already seen, the one claw is the larger because it 

 has grown the faster; it has a higher "coefficient of growth," and 

 accordingly, as age advances, the disproportion between the two 

 claws becomes more and more evident. Moreover, we must assume 

 that the characteristic form of the claw is a "function" of its 

 magnitude ; the knobbiness is a phenomenon coincident with 

 growth, and we never, under any circumstances, find the smaller 

 claw with big crushing teeth and the big claw with Httle serrate 

 ones. There are many other somewhat similar cases where size 

 and form are manifestly correlated, and we have already seen, to 

 some extent, how the phenomenon of growth is often accompanied 

 by such ratios of velocity as lead inevitably to changes of form. 

 Meanwhile, then, we must simply assume that the essential difference 

 between the two claws is one of magnitude, with which a certain 

 differentiation of form is inseparably associated. 



* Cf. H. Przibram, Scheerenumkehr bei dekapoden Crustaceen, Arch. f. Entw. 

 Mech. XIX, pp. 181-247, 1905; xxv, pp. 266-344, 1907; Emmel, ibid, xxii, p. 542, 

 1906; Regeneration of lost parts in lobster, Bep. Comm. Inland Fisheries, Rhode 

 Island, XXXV, xxxvi, 1905-6; Science (N.S.), xxvi, pp. 83-87, 1907; Zeleny, 

 Compensatory regulation, Journ. Exp. Zool. ii, pp. 1-102, 347-369, 1905; etc. 



t Lobsters are occasionally found with two symmetrical claws: which are then 

 usually serrated, sometimes (but very rarely) both blunt-toothed. Cf. W. T. Caiman, 

 P.Z.8. 1906, pp. 633, 634, and reff. 



