266 BULLETIN OF THE 



on a ring of the rattle. A living specimen of this snake, kept for a year 

 or more, would take to rattling on the floor whenever he was irritated. 

 The sound was made by the terminal inch of the tail, this part being 

 swung from side to side in the segment of a circle, so that the tip 

 might strike downward. The result was a tolerable imitation of that 

 made by a small rattlesnake. 



Both Copperhead and Moccasin bear evidence of union between cap 

 and scales. All the specimens have two scales fused above and two 

 below the button ; some show that more have joined the two above, 

 and that one or more of the laterals has been included on the sides. 



The testimony of the embryo is to the effect that the rattlesnakes 

 were derived from forms in which the terminal vertebras were not 

 fused into a terminal bone. There seems to be no radical difference, 

 in the earlier stages of the end of the tail, between the above men- 

 tioned as well as other non-crotalophorus forms and Crotalus. So much 

 divergence in the number and shape of the caudal vertebrae occurs 

 in the various genera, that these features become matters of secon- 

 dary interest in a general comparison. In the later development the 

 rattlesnake goes farther than any of the others. The bone at the 

 end of the column is of the same nature throughout the Ophidia. 

 On Crotalus it eventually contains a greater number of vertebrae, 

 there is a greater enlargement of the mass, and in devoting it ex- 

 clusively to shaking the rattle, instead of striking upon objects, a difi'er- 

 ent use is made of it. In front of the rattle the neural spines incline 

 forward, possibly a consequence of the function of the tail. This in- 

 clination has little weight when compared with forms like Ancistrodon, 

 where the spine is so low. Similar leaning toward the head occurs in 

 the Hydrophidse and in Ogmophis, a Tertiary fossil of uncertain affinity. 

 So far as the vertebrae are concerned, they point to no special one of 

 the recent allies as representative of the stock from which the rattle- 

 snakes have sprung. 



With the button there is but little more success. While it miaht 

 possibly have been formed or enlarged by fusion of scales with the cap, 

 there is really no reason to suppose scales were formed on the end of the 

 tail only to be lost again. In fact, embryonic data favor the conclu- 

 sion that it was formed by simple enlargement, or expansion of the cap 

 itself. A cap that by its shape would be mechanically held to its suc- 

 cessor might be produced by slight changes in that of any one of a num- 

 ber of species of the family, in addition to those figured. Shape is the 

 important feature in the retention of the series of caps. This, in the 



