262 BULLETIN OF THE 



been set free with the first slough, holding only by the collar ; and if 

 the snake had been allowed to live a little longer, the second sloughing 

 would have discovered the third button perfected, clasped by the sec- 

 ond ring, the latter pushed back and loosened from the balance of the 

 epiderm. Of the second ring the narrower posterior extension is quite 

 empty ; its anterior chambers are closely filled with the tumid skin, 

 the loss of the ring being prevented in this manner, while the outer 

 swelling of the new button is crowding it backward. A considerable 

 shrinkage of the skin takes place after the moult ; it is insufficient to 

 allow the ring to slip off, though admitting of great freedom of motion. 

 In front of the border of the second ring, Fig. 5, lies the fold, shrunken 

 by alcohol in the specimen, by which the ring was displaced, and which 

 was to become the largest chamber of the next succeeding. This fold is 

 usually hidden by the epiderm attached to the ring, as in Fig. 6, until 

 the operation of sloughing has been finished. The mass of bone oc- 

 cupies the place of eight or more of the vertebrae in this stage, the lines 

 of separation being still noticeable to some extent. By a longitudinal 

 section the cord and vessels are disclosed in their original positions, sur- 

 rounded now by spongy bone, in which the cavities radiate from the 

 centre toward the surfaces. On the upper and lower faces there is less 

 indication of the composition. 



Figures 7 and 8 were taken from a large specimen of Crotalus hor- 

 ridus, Linn. In it the traces of the vertebraj in the terminal bone are 

 almost obliterated ; the bone has thickened, pushed forward at the edges, 

 and otherwise enlarged. Along with this there has been an excessive 

 development of the muscles of the tail. The rattle is entire, of eleven 

 rings and a button. The hinder seven of the rings belong to the period 

 of the snake's most rapid growth ; they form the "tapering rattle" com- 

 mon to the young individuals, formerly used in classification of the 

 species by some authors. Four of the rings and the button pertain to 

 a part of the creature's life in which the gain in size was much less 

 rapid ; they form the " parallelogramic rattle " of the same writers. 

 The mistaken use of these features in specific diagnoses no doubt arose 

 from study of incomplete rattles. The change from the taper to the 

 more nearly parallelogramic takes place about the seventh ring, — in 

 Sistrurus miliarius often with the sixth, with the larger species fre- 

 quently with the eighth, — and affords the means of obtaining an ap- 

 proximate idea of the comparative age of the owner of the series of 

 rings. The figures show the rattle as commonly held by the snake 

 when crawling. In a single series of rings there is much variation in 



