THE OUTDOOR WORLD. 



89 



An Interesting Crab's Claw. 



BY ROBERT GREENLEAF LEAVITT, NEW 



JERSEY STATE NORMAL SCHOOL 



AT TRENTON. 



The editor of this journal has kindly 

 given me a deformed crab's claw in 

 which I became interested through 

 the publication of a brief mention of it 

 in "St. Nicholas" for December, 1907. 

 The claw is interesting because it goes 

 with a number of other things to throw 

 a somewhat new light, or let us say a 

 little light from a new direction, upon 

 the process by which an animal's body 

 is built up. If the principle of the 

 matter is pointed out, readers of The 

 Guide to Nature will be likely to find 

 other examples ; and if they will 

 carefully describe, and especially if 

 they will carefully illustrate, their dis- 

 coveries and publish them, they may 

 make real contributions to science. 



The claw was found at Stonington, 

 Connecticut, and brought to notice by 

 Miss E. P. Loper. The remarkable 

 feature is an addition, in the form of a 

 small pincer, near the extremity of the 

 movable joint or dactyl. This small 

 organ copies each detail of the larger 

 one faithfully as to the shape and re- 

 lative size of the two parts, as to the 

 teeth and as to the nature and col- 

 oration of the hard material composing 

 the extremities of the pincer-arms. 

 Only in one respect is there an es- 

 sential difference : in the small pincer 

 the dactyl is not movable at the base, 

 as it is in the larger one. The pincer 

 is therefore useless. Indeed it must 

 have been an inconvenience to its pos- 

 sessor. 



Such malformations have several 

 times been noted in the claws of lob- 

 sters. It seems pretty certain that they 

 arise in the healing' of wounds inflict- 

 ed when the animal is freshly moulted 

 and its limbs are soft. 



It is well known that crustaceans 

 have a good deal of the power of re- 

 generation. Whole limbs may be 

 replaced. In a case like the one before 

 us, it was to have been expected that 

 the wound would fill up. It was not to 

 have been expected that the growth 

 from the torn edges would take the 

 form of a nearly perfect claw. 



The new member imitates another, 

 previously existent, organ. Such ab- 

 normal mimicry, or borrowing of 

 character by one region from another, 

 has been called by "William Hateson 

 of England, Homoeosis. He detected 

 it in several monstrous formations ; for 

 example, in turbots displaying upon 

 the lower surface features proper to 

 the upper side. Weismann, the Ger- 

 man zoologist, has argued that the 

 markings on certain segments of a 

 species of caterpillar originated in a 

 like manner by transference from other 

 segments. The present writer has 

 pointed out (Botanical Gazette, Jan- 

 uary, 1909) the probable derivation of 

 some normal structures in plants by 

 Homoeosis, or translocation of char- 

 acters. In cases noted in plants 

 Homoeosis has, apparently, proved to 

 be hereditary. 



The special interest of our crab's 

 claw lies, as already suggested, in its 

 relation to the development of form 

 in growing parts, and its bearing on 

 the theory of such development pro- 

 posed by Weismann. 



The evolution of the body with its 

 myriad cells of different kinds — nerve, 

 muscle, bone cells, etc., etc. — and with 

 its numerous and often complex or- 

 gans, all developed from a minute egg 

 of simple form, in which the features 

 of the adult organization are utterly 

 absent, is a most mysterious process. 

 \\ ny do all the parts develop in their 

 proper sequence and compose a har- 

 monious whole rather than a shapeless 

 mass of cells ? No one can as yet 

 answer this question. 



The evolution is guided from within, 

 for the growing organism is not run 

 in a mold but assumes its shape with- 

 out the aid of external formative pres- 

 sures. The process is supposed to be 

 fundamentally a mechanical one, and 

 theories of the mechanism have been 

 attempted. Most speculators have 

 imagined that small bodies exist in 

 the cells, capable of determining the 

 forms of the bodily members — germi- 

 nal bodies, gemmules (i.e., little buds) 

 or determinants. Each part of the 

 bodv is supposed to have its particu- 

 lar germinals. It may be supposed 

 that in the egg all the determinants 



