382 



REPORT OF NATIONAL MUSEUM, 1893. 



Fig. 26. 



TAIL END OF EMBRYO OF MAS- 

 SASAUGA. 



Side view. Three times 

 natural size. 



(After Garmun.) 



tho organ (fig. 24). It is tlien seen that eaeli "ring" is in reality a 

 "button" that fits over aiul conceals tho terminal portion of the fore- 

 going (proximal) joint, leaving exposed only the hasal swelling, the 

 ring. The joints are consequently a series of partly overlapping thin 

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

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

 oV)served that the free edge of the cone is bent inward and fits into the 

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

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

 the body. The opening being narrower than this swelling, the 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 furthermore be noted, upon actually dissecting the tail end 

 of the body, that the basal cone of the rattle forms the horny cover of 

 a strong thickening of the skin which, in turn, 

 envelops a more or less cone-shaped compressed 

 bone. This bone terminates the vertebral col- 

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

 larged and fused together into one. 



Upon this dermal thickening surrounding the 

 terminal bone, the epidermal horny capsule is 

 evidently formed. The latter, in the same man- 

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

 growth l)ecomes detaclied from tho secretory layer, and a new epiderm 

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

 the outer skin results in the well-known j)rocess of sloughing, the pecu- 

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

 thickness and strength prevents its slipping off 

 in the same manner. It- is consequently pushed 

 out from the end of the tail closely clasping 

 around the median constriction of the new cone 

 which now appears externally as the basal " ring." 

 Prof. Samuel Garman has carefully worked out 

 and l)eautifully illustrated the successive stages 

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

 the perfected organ in the full-grown snake, and from his paper* the 

 following account is mainly taken : 



In very early embryos of the Ground Kattlesnake, Sisfrunis milia- 

 riun, some of them already 3 inches long, the tail was not yet furnished 

 with scales, though the 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 S[)ecies, the Massasauga, iS. c<(tr)i((ti(s, however, which 

 were ohler aiul twice as largo, showed a distinct promise of the future 

 rattle in tlie shai»o and size of the terminal ca]), or barton (figs. 2(i, 1*7), 



*The Rattle of the Hattli>sii;ili(\ IliiUetiu I\Iu.s. Couij). ZoiJl. Harv. Coll., Xlll, 

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





Fig. 27. 



DIAGRAMMATIC LONGITUDINAL 



SECTION OF FIG. 2G. 



