24 A JOURNEY IN BRAZIL. 
of their first phases of development. A complete embryology 
of the alligator would give us not only the natural classifica- 
tion of reptiles as they exist now, but might teach us some- 
thing of their history from the time of their introduction 
upon earth to the present day. For embryology shows us 
not only the relations of existing animals to each other, but 
their relations to extinct types also. One prominent result 
of embryological studies has been to show that animals in 
the earlier stages of their growth resemble ancient represent- 
atives of the same type belonging to past geological ages 
The first reptiles were introduced in the carboniferous epoch, 
and they were very different from those now existing. 
They were not numerous at that period ; but later in the 
world's history there was a time, justly called the ' age of 
reptiles,' when the gigantic Saurians, Plesiosaurians, and 
Ichthyosaurians abounded. I believe, and my conviction is 
drawn from my previous embryological studies, that the 
changes of the alligator in the egg will give us the clew to 
the structural relations of the Reptiles from their first crea- 
tion to the present day, will give us, in other words, their 
sequence in time as well as their sequence in growth. In 
the class of Reptiles, then, the most instructive group we 
can select with reference to the structural relations of the 
type as it now exists, and their history in past times, will be 
the alligator. We must therefore neglect no opportunity oi' 
collecting their eggs in as large numbers as possible. 
k ' There are other animals in Brazil, low in their class to 
be sure, but yet very important to study embryologically, on 
account of their relation to extinct types. These are the 
sloths and armadillos, animals of insignificant size in our 
days, but anciently represented in gigantic proportions. 
The Megatherium, the Mylodon, the Megalonyx, were some 
