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. Ail 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 vertebre 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 vertebre 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 vertebre, 
there is a greater enlargement of the mass, and in devoting it ex- 
clusively to shaking the rattle, instead of striking upon objects, a differ- 
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 Hydrophidee and in Ogmophis, a Tertiary fossil of uncertain affinity. 
So far as the vertebree 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 might 
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 
