6 
248 [Dee, 15, 
Cope. ] 
their adaptation to aération in water, and then by their successive de- 
partures from this type in connection with the faculty of breathing air. 
The same succession of structure is traversed by the embryos of the ver- 
tebrates, the number of stages passed being measured by the final status 
of the adult. This transition takes place in the Batrachia later in devel- 
opment than in any other class. Now, it is well known that the transi- 
tion or metamorphosis may be delayed or encduraged by suppression of 
use of the branchial and encouragement of use of the pulmonary organs 
or the reverse. 
The aquatic respiration of tadpoles may be indefinitely prolonged by 
preventing their access to the surface, and it is known that in nature the 
size or age of the larva at time of metamorphosis may vary much in the 
same species. If perennibranchiates (Stren e.g.) are deprived of their 
branchia, they will aérate blood by the lungs exclusively, and there is no 
reason to doubt that by use of these, and disuse of the branchia, aérial 
respiration might become the habit of the animal. It is also easy to per- 
ceive that geologic changes would bring about a necessity for precisely 
this change of habit. This occurred in the period of tie coal measures, 
where large fresh water areas were desiccated, and it was precisely at this 
period that many air breathing Batrachians originated and had a great 
development. ; 
& The rattle of the Rattlesnake. 
Nearly all of the larger harmless snakes which live on the ground have a 
habit of throwing the end of the tail into violent vibrations when alarmed or 
excited, with the view of alarming a supposedenemy. Among Coronelline 
snakes, Ophibolus triangulus possesses it; among the water snakes, 7’ropt- 
donotus sipedon. Inthe typical Colubrine group the black snake, Bascanium 
constrictor isan example; Pityophis say? also shakes the tail violently. 
The copperhead (Ancistrodon contortriz) and the moccasin (A. piscivorus) 
(fide Giinther) have the habit in a marked degree. Among the rattle- 
snakes it is a means of both warning and defence, in connection with the 
rattle which they carry. 
In the structure of the end of the tail of harmless snakes, we see a 
trace of the first button of the rattle in a horny cap that covers the ter- 
minal vertebree. 
In the venomous genera, it is conspicuous in Lachesis especially, reach- 
ing a considerable length and having a lateral groove. In the plate- 
headed rattlesnakes (Crotalus) this corneous cap is inflated into a button 
with lateral groove, and in some of them possesses only one or two but- 
tons or joints. In the perfected rattlesnakes (Caudisona) not only are the 
segments numerous and inflated, but a number of the terminal caudal 
vertebr are greatly enlarged vertically, and codssified into a mass.* This 
is important from the fact that the rattlesnakes are the most specialized 
of all snakes, standing at the head of the order, and as such, on the prin- 
cipal of acceleration present the greatest amount of grade nutrition. 
Now it appears to me, that the constant habit of violent vibration in a 
“See good figures of this structure in Zeitschr. f, Wissensch. Zoologie, VIII, Tab. 12. 
