THE COMMON FROG 
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\ HAT isa Frog? At first, almost all persons will think, on 
meeting with this question, that they can answer it readily 
and easily. Second thoughts, however, will show to most that 
such is by no means the case. 
Indeed many a man of education and culture will find himself 
entirely at a loss, if suddenly called upon for a reply to what is 
in fact a problem by no means easy of solution. 
“The Frog is a small saltatory Reptile” will probably be the 
reply of the majority. But zs it a Reptile? At any rate it begins 
life (in its Tadpole stage) like a Fish! 
By the great Cuvier, however, as by very many naturalists 
since, it has been regarded as a Reptile and classed with Lizards, 
Crocodiles, and Serpents ; and yet it may be a question whether 
the murine affinity connubially assigned to it in the Nursery tale, 
be not the lesser error of the two. 
If the Frog was only known by certain fossil remains it would 
be considered one of the most anomalous of animals. 
Many persons are accustomed to make much of the distinctive 
peculiarities of the human frame. In fact, however, Man’s 
bodily structure is far less exceptional in the animal series, is far 
less peculiar and isolated than that which is common to Frogs 
and Toads, 
The number and nature of both the closer and the more remote 
allies of the Frog ; its distribution both as to space and as to 
time ; its relationships whether of analogy or affinity * to very 
different animals ; its bony frame-work ; its muscles and nerves ; 
its brain and sense-organs ; its respiratory and excretory struc- 
tures ; its various changes from the egg to maturity, together 
with peculiarities of habit in allied forms ; are all matters which 
will well repay a litile attentive consideration. 
Indeed it is probable that no other existing animal is more 
replete with scientific interest of the highest kind, than is the 
Frog. 
About it are gathered biological + questions which bear upon 
the origin of species, and upon the course and mode of or- 
ganic development, as well as other speculative problems to 
which answers are as yet far to seek. 
If it is a fact that all the various species of animals have arisen 
through ordinary genera'i n one from another by a process of 
development, the life history of the Frog may with reason be 
expected to have some bearing upon such a process, since 
every Frog begins its free existence with the organisation of a 
Fish, and after undergoing a remarkable ‘* Metamorphosis,” 
attains the condition of an air-breathing quadruped, capable of 
easy and rapid terrestrial locomotion, 
There is a matter with respect to which the zoologist can 
hardly avoid regarding the botanist with envy. The creatures 
sought after by the latter may be rare or inhabitants of stations 
difficult of access, but at any rate they are incapable of flight or 
concealment, and specimens of some kind or other generally 
present themselves in plenty. 
On the other hand not only does the townsman of a thickly- 
peopled land like our own, often meet with fewer animals in his 
couhtry walks than he anticipated, but the explorer of tropical 
lands and virgin forests has frequently to endure disappointment 
from the contrast between the richness of a known local fauna 
and the little to be actuaily seen of the animal population of the 
place. ‘ 
Frogs and Toads, however, are often enough seen both at 
home and abroad, and when perceived generally fall a far more 
ready prey to the collector than do the swift-running Lizards and 
small Beasts which are the commonest ground-animals met with 
besides. The group is also rich in species as well as in indi- 
viduals, and it is spread over the far greater part of the habitable 
globe. Nevertheles Frogs and Toads have few admirers even 
amongst professed zoologists, and meet with no little neglect. 
While the term ‘‘ Ornitholozist” + is familiar to everyore, and 
the tile *‘ Erpetologist” § is so to all naturalists; the name 
‘‘ Batrachologist ” || has not yet been conferred on or assumed 
by any one worker in Science. 
* Analogous relationship refers to the uses to which parts are put. Rela- 
tionship of affinity refers either to such a relationship as that of kindred or to 
an ideal a‘finity reposing on similarities of structure. 
+ Biological questions are questions referring to living beings. “ B’ology 
1 eve the science which treats of all living things, including both plants and 
nimals. 
t “Opudoc, a bird, and Adyoe, a discourse, 
§ 'Epmeroy, a reptile, and Adyor, 
i Barpaxog, a frog, and Adzog. 
a) NATURE | 
[Océ 2, 1873 | 
Economically, Frogs are of little esteem in England save 
occasionally for bait and as the staple food of certain rare and 
interesting animals preserved in our menageries. Our American — 
cousins indeed have given one more evidence of their French 
sympathies by the introduction of the Frog into their cuésine, 
and, as suits that land of the longest rivers and the largest lakes, 
it is no less a creature than the gigantic Bull-frog which figures 
in the menu of Transatlantic gourmets. ; 
If zoologists and economists have neglected the Frog, the 
same assertion can by no means be made with respect to physio- 
logists. 
‘The Frog is the never-failing resource for the physiological 
experimenter. It would be long indeed to tell the tee of 
much-enduring frogs in the cause of Science! What Frogs | 
can do without their heads? What their legs can do without 
their bodies? What their arms can do without either head or 
trunk ? What is the effect of the removal of their brains? How 
they can manage without their eyes and without their ears? 
What effects result from all kinds of local irritations, from chok- 
ings, from poisonings, from mutilations the most varied? These 
are the questions again and again addressed to the little animal 
which perhaps more than any other deserves the title of *‘ the 
Martyr of Science.” i 
To return to our question at starting, ‘‘ What is a Frog?” 
To answer this, it will in the first place be well to make a cer- 
tain preliminary acquaintance with the frog absolutely. 
Fic, 1.—The Common Frog, Rana tenporaria, 
Secondly, to study those creatures which are most like it, 
and are, therefore, as we shall directly see, its ‘class fellows,” 
living and fossil. 
Thirdly, to investigate its anatomy so far as to be able to in- 
stitute fruitful comparisons between its organisation and that of 
all other creatures belonging to the same great primary group of 
animals to which it pertains. 
Fourthly, to sum up the results in a series of successively 
wider and wider comparisons, and by the light thence derived to 
answer as fully as the present state of Science allows the question 
first asked, 
We shall then be able to answer that question, because we shall 
have ascertained how various parts of this creature form one 
organic whole as a system of mutually related structures ; and 
how this whole and its parts are related to the entire series of — 
animal existences from the monad up to man. Then, and then 
only shall we be able to say what a frog is. , 
In the first place it is necessary to acquire a general notion of 
the way in which animals are distinguished and segregated into 
groups, as well as the general system of arrangement of those 
groups and the mode of Lestow ng names which has been adopted 
by zoologists in common with botanists. 
When we have acquired an adequate general notion of zoolo- 
gical classification we shall be able to see with what creatures 
the Frog is now admitted to be, in various degrees, allied. } 
The whole mass of animals of all kinds from man down to 
the lowest animalcula) is spoken of by the fanciful term Ring- 
