174 
[Gavman. 
by the embryo of the ordinary species producing living young, as 
the latter may be said to have gone farther than that of the egg-lay- 
ing species. If the cap were complete in this stage (figs. 1 and 2) it 
would be lost with the slough from the body, and a rattle would not 
be possible. 
Figs. 3 and 4 are taken from a specimen shortly after birth. 
The changes, as compared with the preceding, are very marked. In 
addition to the part of the cap that was present in the earlier stage, 
we find an anterior, wider portion, a shoulder or swelling, sepa- 
rated from the posterior section by a slight constriction, as if subse- 
quent growth in this part of the tail had demanded the interpolation 
of a wider band to contain a greater bulk, and as if increase in 
length of the button had crowded the cap back from the scales, com- 
pelling expansion at its anterior margin. That the increase in size 
of the cap is not entirely, or even mainly, due to a backward growth 
from its anterior margin will be seen from what follows. In a sec- 
tion of this stage, fig. 4 , the hinder seven or eight of the vertebrae 
are seen to have coalesced into a single mass, showing a disposition 
to expand so as to obliterate the processes and lines of demarcation 
of the bones of which it is composed, but which are still plainly in- 
dicated. This composite bone may be called the shaker. Through 
its own expansion, and the thickening of the skin around it the mus- 
cles between the bone and the skin are on the way to disappear. The 
muscles controlling the shaker lie in front of it and are strongly 
developed. This stage has the completed button. As yet the snake 
has no rattle. After the first sloughing he finds himself in posses- 
sion of one made up of a single ring and the button. The ring is 
the cap with which he was born ; it has been freed from the button 
and pushed backward, far enough to make room for the anterior 
swelling of a new cap between itself and the scales, and there it clings 
loosely but securely to its successor. The process is the same for 
each succeeding ring. 
Figs. 5 and 6, from a specimen which had displaced the first 
cap and was in the act of displacing the second, illustrate the man- 
ner in which the ring is moved back as the new cap is formed. At 
the time of the new growth, the tail immediately in front of the but- 
ton has the appearance of being swollen, and its owner is more than 
ordinarily sensitive in this portion of his body. The milky appear- 
ance in the skin seems to mark a period of rapid growth. In con- 
sequence of the latter, the swelling, and the limited space within 
