22 A JOUKNEY 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- 

 minsd. L. A. 



