INTRODUCTION. XXVIL 
account of previous association. The name proposed for the species grouped 
under Crotalophorus of Gray, Holbrook, and others, but not of Linné or 
Gronow, is Sistrurus (ceotpor, a rattle). 
JATRACHIA., 
The Batrachians are vertebrates, such as the Crecilians, Salamanders, 
Toads, and Frogs, the most of which are affected by a metamorphosis, 
during which a branchial and fish-like respiration is changed to one in 
which the main dependence is placed on lungs. Whether breathing by 
means of gills in the earlier stages, or by lungs in the later, these animals 
are possessed of a supplementary cutaneous respiration. It is by the aid 
of the latter that they are enabled to pass periods of several months to a 
couple of years buried in the earth or mud during hibernation. Moisture 
is at all times absolutely necessary; deprived of it they soon die. The 
skin is naked, either smooth or rough. In cases the skin over the whole 
body is glandular; in others the cutaneous glands are aggregated in par- 
ticular portions of the body, as the parotoids of Toads and some Sala- 
manders. A few of the snake-like batrachians have rudimentary scales 
hidden in the skin. The slough is stripped off more or less entire, and 
generally eaten. The gills are retained by certain forms throughout their 
whole existence; in these, however, the lungs are partially developed, and 
the respiration is at the same time branchial and pulmonary. The heart 
has but a single ventricle, and the atria are incompletely separated. 
There are two occipital condyles. For the most part, the very young 
feed on vegetation; in such the intestine is elongate. Those beginning 
their independent existence after the tadpole stage has been passed, and 
the later stages of all members of the class, are carnivorous. The prey 
is swallowed entire. There are a few instances in which the embryo is 
developed and the young hatched in the oviduct. Commonly the eggs are 
fertilized externally, as or after they are laid. Eggs of batrachia have been 
favorites of embryologists in their researches; it was in them Prevost and 
Dumas first noticed the cleavage masses, and in them Newport saw the 
spermatozoon creep through the outer envelopes to the yolk. We know no 
species of which the bite is poisonous. The nearest approach to venom is 
in the acrid, milky secretion of the parotoids, which produces considérable 
irritation when brought in contact, with the membranes of eyes or mouth, 
