GENERAL CHARACTERISTICS OF BATRACHIANS. 297 
temperature of the water, exhibit signs of life by first undergoing 
what is known as “ segmentation,” or sub-division, and by the 
appearance of the “ primitive groove,”’ which may be seen by the 
help of a microscope. The margins of this groove fold upwards 
until they meet above ; thus a kind of tube is formed, the interior 
of which becomes in time the spinal cord. Below the “ primitive 
groove” is developed a “gelatinous rod,” which gradually 
becomes the backbone. The process just described is common to 
every kind of egg which produces a vertebrate animal. 
The Frog’s (and Toad’s) egg now, even by the unassisted eye, 
is seen to lose its roundness of shape and to become elongated, 
and then, sometimes in turn and sometimes concurrently with 
each other, the following changes take place: (1) a head, tail, 
and organs of adhesion appear; (2) branchiz are developed on 
each side of what may be called the neck; (3) slight movements 
may be noticed; (4) nostrils or olfactory organs come into ex- 
istence ; (5) the branchiz have so grown that the circulation of 
the blood may be seen in them by the help of a microscope; (6) 
frequent movement of the embryo from a curved to a straight 
position, and vice versd (Fig. 77, c and d); (7) these movements 
or jerkings become so vigorous that the envelope is broken 
and the tadpole is free (Fig. 77, e and f); (8) soon after the 
tadpoles are hatched, they may be seen in rows and bunches 
adhering, by means of the organs provided for the purpose, to 
some substance, such as a weed, a stick, or a stone; (9) the head 
of the young animal is large, the body round, and the tail long 
and strongly compressed laterally (Fig. 77, g); (10) the 
creature’s life is now very like that of a fish, and its food is 
chiefly vegetable matter; (11) the branchize grow in size, and 
are very plumose (Fig. 77, h); (12) the branchize are gradu- 
ally absorbed, and are replaced by “ gill-filaments”’ along each of 
the “ branchial arches,” 7.e., the spaces between the six openings 
on each side of the neck; (13) the animal, which is provided 
with horny and slightly protruding jaws, now begins to feed wpon 
animal food, such as small aquatic creatures, dead worms, and the 
like ; (14) the eyes become noticeable; (15) the tadpole, if pro- 
vided with plenty of food, fresh water, and warmth, grows very 
quickly ; (16) the hind legs bud and are produced (Fig. 77, 7 and 
