24 A JOURNEY IN BRAZIL. 



of their first phases of development. A complete emoryology 

 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 of 

 collecting their eggs in as large numbers as possible. 



" 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 



