22 A JOURNEY IN BRAZIL. 
most striking examples, but there are others quite as much 
so, though not as familiar. The frog, for instance, in its 
successive stages of development, illustrates the comparative 
standing of the orders composing the class to which it 
belongs. These orders are differently classified by various 
naturalists, according to their individual estimate of their 
structural features. But the growth of the frog, like that 
of the insects, gives us the true grade of the type.* There 
are not many groups in which this comparison has been 
carried out so fully as in the insects and frogs ; but where- 
ever it has been tried it is found to be a perfectly sure test. 
Occasional glimpses of these facts, seen disconnectedly, have 
done much to confirm the development theory, so greatly 
in vogue at present, though under a somewhat new form. 
Those who sustain these views have seen that there was a 
gradation between animals, and have inferred that it was a 
material connection. But when we follow it in the growth 
of the animals themselves, and find that, close as it is, no 
animal ever misses its true development, or grows to be 
anything but what it was meant to be, we are forced to 
* In copying the journal from which these notes are taken, I have hesitated 
to burden the narrative with anatomical details. But for those who take 
an interest in such investigations it may be well to add here that the frog, 
when first hatched, is simply an oblong body, without any appendages, and 
tapering slightly towards its posterior end. In that condition it resembles the 
Cecilia. In its next stage, that of the tadpole, when the extremity has 
elongated into a tail, the gills are fairly developed, and it has one pair of 
imperfect legs, it resembles the Siren, with its rudimentary limbs. In its 
succeeding stages, when the same animal has two pairs of legs and a fin around 
the tail, it recalls the Proteus and Menobranchus. Finally the gills are 
suppressed, the animal breathes through lungs, but the tail still remains ; it 
then recalls Menopoma and the Salamanders. At last the tail shrinks and 
disappears, and the frog is complete. This gives us a standard by which 
the relative position of the leading groups of the class may safely be deter- 
mined. L. A. 
