382 REPORT OF NATIONAL MUSEUM, 1893. 



tbe organ (fig. 24). It is tlien seen tbat each "ring" is in reality a 

 "button" tbat fits ov.er and conceals tbe terminal portion of tbe fore- 

 going (proximal) joint, leaving exposed only tbe basal swelling, tbe 

 ring. Tbe joints are consequently a series of partly overlapping tbin 

 horny capsules or "cones." These "cones" have a wavy outline con- 

 sisting of two or three swellings and two constrictions. It will also be 

 observed that the free edge of tbe cone is bent inward and fits into tbe 

 basal groove of tbe preceding cone, so that tbe basal swelling of tbe 

 more distal cone clasps around tbe second swelling of tbe one nearer 

 tbe body. Tbe opening being narrower than this swelling, tbe two cones 

 are effectually linked together by means of a kind of restricted ball- 

 and-socket articulation, modified by the shape of the joints. 



It will furtbermore be noted, uj^on actually dissecting the tail end 

 of tbe body, tbat tbe basal cone of the rattle forms tbe horny cover of 

 ^...^-^.^-e. ^ strong thickening of tbe skin which, in turn, 

 '(^ffr^^^^L envelops a more or less cone-shaped compressed 

 '^^^^^^^x. t)Owe- This bone terminates the vertebral col- 

 umn, being in fact the 7 or 8 last vertebrie en- 



Fig 26. 



TAIL END OP EMBRYO OF MAS- largcd aud fuscd together into one. 



SASAUGA. Upon this dermal thickening surrounding tbe 



Side view. Three times j.„-ii xi -i ii i- 



natuiai size. terminal bone, the epidermal horny capsule is 



(After Garman.) c vldeii tly formcd. Tbe latter, in the same man- 



ner as the rest of tbe epidermis in tbe snakes, in tbe course of its 

 growth becomes detached from tbe secretory layer, and a new epiderm 

 is formed beneath it, but while on the rest of tbe body this renewal of 

 the outer skin results in tbe well-known process of sloughing, the pecu- 

 liar shape of tbe horny capsule of the end of the body and its greater 

 thickness and strength prevents its slipiiing off" 



in the same manner. It is consequently pushed z-^" ^^'^TTXTTT^ 

 out from tbe end of tbe tail closely clasping \^^-^UlUlU-}<,^ 1^ 

 around tbe median constriction of tbe new cone ^ — u-.-...,-^...^.-,---,--..^..-^ 

 which now appears externally as the basal "ring." Fig. 27. 



Trof. Samuel Garman has carefully worked out diagrammatic longitudinal 



^ section of fig. 26. 



and beautifully illustrated tbe successive stages 



of tbe growth of tbe rattle from the first indication in the embryo to 

 tbe perfected organ in tbe full-grown snake, and from bis pai^er* the 

 following account is mainly taken : 



In vei-y early embryos of the Ground Rattlesnake, Sistrurus milia- 

 rius, some of them already 3 inches long, tbe tail was not yet furnished 

 with scales, though tbe entire body was well provided. Outwardly 

 the tail was short, thick, blunt, slightly compressed, but with no indica- 

 tion of the characteristic feature so prominent after birth. Embryos 

 of a nearly allied species, tbe Massasauga, 8. catenatus, however, which 

 were older and twice as large, showed a distinct promise of tbe future 

 rattle in the shape and size of tbe terminal cap, or button (figs. 26, 27), 



*The Rattle of the Rattlesnake. Bulletin Mus. Comp. ZoOl. Harv. Coll., Xlii, 

 No. 10, pp. 259-268, pis. i, 11. August, 1888. 



