a Pe Py 2 Paid 
Oct..16, 1873) 
adhesion) just behind the mouth, with six openings on each side 
of the neck (Fig. 3, c/+-c/*), and with a pair of rudimentary 
_ external gills (Fig. 3, 471 and 4r*). These openings are termed 
visceral clefts,” which lead from the exterior into the throat, as 
already described. The solid pillars (or intervals) between the 
clefts, z.2., the ‘‘ visceral arches,” become furnished with gills, * 
or branchiz, and are therefore called ‘‘ branchial arches.” The 
eggs are hatched towards the end of April, and the tadpole 
emerges in the stage represented at Fig. 2, 1. It has a relatively 
large head, a rounded body, and a long tail, by lateral undula- 
tions of which the little creature swims about. From behind 
the head, on each side, jut forth external branchie as a small 
plume-like structure, but no limbs are visible. 
As the tadpole grows the external plumose gills at first greatly 
enlarge (Fig. 2, 2 and 22), but afterwards become gradually 
absorbed, and are succeeded by short gill-filameats, which are 
ai’ 
eto EA 
Fic. 5.—A, Pachybatrachus robustus, nat. size; B, interior of the 
mouth of ditto. 
developed along each of the branchial arches. These latter 
filaments du not appear externally, and indeed a membrane, 
termed the operculum (Fig. 3, of), is developed from the front 
of each series of branchial apertures, and which, extending back- 
wards by degrees, ultimately covers over and conceals them. 
Little by little the limbs bud forth and grow, the hind ones 
being the first visible because the fore limbs are for a time con- 
cealed by the opercular membrane. As the legs grow, the tail 
becomes absorbed (Fig. 2, 7), not falling off, as some suppose. The 
gills also disappear, and the branchial apertures close, that on the 
right side first becoming obsolete by adherence of the operculum 
to the skin of the body. ’ 
As the gills diminish and cease to serve the purposes of respi- 
- ration, lungs at the same time become developed in an inverse 
* Gills (or branchie) are delicate processes of skin richly supplied with 
sminute blood-vessels, whereinthe blood becomes exposed to the purifying 
-action of the air dissolved in the water. 
NATURE BIT 
ratio, and the tadpoles absolutely require to come to the surface 
to breathe. 
The process, from the hatching to the acquisition of the minia- 
ture form of the adult, may be accelerated or retarded by elevation 
or depression of the temperature. The frog more than doubles its 
bulk in its first summer.* The young tadpole has at first a very 
small mouth placed beneath the head and not at its anterior ter- 
mination ; it is also for a time provided with a sort of beak 
formed of two little horny jaws. 
The food of the tadpole, quite unlike that of the adult, con- 
sists largely (especially in its earlier stages) of vegetable sub- 
stances. 
Having now made acquaintance with the Frog considered 
absolutely, or by itself, and also clearly seen that it is a member 
of the Vertebrate Sub-kingdom, we may enumerate the principal 
primary sub-divisions (Classes) of that Sub-kingdom, and enume- 
rate such of the next smaller groups (Orders) as more or less 
nearly concern the subject of this work—the Frog. 
The Vertebrata are divided into five great Classes :—(I), 
Mammatia (Man and Beasts) ; (II.), Aves (Birds) ; (III.), Rep- 
cilia (Reptiles, z.e. Crocodiles, Lizards, Serpents, and Tortoises) ; 
(IV.), Batrachia (Amphibians, i.e. Frogs, Toads, Efts, &c.) ; 
and (V.), Pisces (Fishes). 
Of these five classes Birds and Reptiles are classed together 
in a larger group called Sauropsida, because they present so 
many structural resemblances. Similarly Amphibians and Fishes 
are grouped together, and to their united mass thegcommon term 
Ichthvopsida is applied. 
Fic. 6.—The Common Toad (Bu/o vulearis) 
The orders into which the two classes, Mammalia and Aves 
(beasts and birds), are divided, may here be neglected, as we 
sball have little to say respecting them in the following pages. 
There are, however, about twelve orders of beasts, and probably 
some fourteen of birds, 
The class of Fishes has been subdivided into five Orders. 
1. Elasmobranchii (the sharks and rays, or highly organised 
cartilaginous fishes). 
2, Ganoidei, an important order, containing many extinct 
forms, and a few very varied existing ones, such as the mud-fish 
(Lepidosiren), ceratodus, and the sturgeon. 
3. Teleostei, the ordinary or bony fishes, such as the carp, 
sole, perch, &c., and containing a remarkable group called Silu- 
roids, as also the curious little sea-horse—Hippocampus. 
4. Marsipobranchii (the lamprey and myxine, or lowly orga- 
nised cartilaginous fishes). 
5. Pharyngobranchii (the amphioxus, or lancelet). 
Reptiles are arranged in nine different orders, five of which 
are now entirely extinct. They are of living forms :— 
1. Crocodilia (crocodiles). ’ 
2. Sauria (lizards, the Amphisbenz, the little Flying-dragon, 
xc.) 
3- Ophidia (serpents). 
4. Chelonia (tortoises and turtles). 
Of extinct kinds there are :— 
5. Ichthyosauria ; 6, Plesiosauria ; 7, Dicynodontia ; 8, Pteto« 
sauria ; and 9, Dinosauria. 
The remaining class, Batrachia, will require more lengthy con 
sideration, both as a whole and as regards the four orders which 
compose it, and which are called respectively, 1, Anoura; 2, 
Urodela ; 3, Ophiomorpha ; and 4, Labyrinthodonta, 
It will require such consideration, because it is the class to 
which the Frog itself belongs, 
* Parker, Phil. Trans., 1871, p. 172. 
