14 A JOURNEY IN BRAZIL. 
yet these investigations include so small a number of repre- 
sentatives from the different classes of the animal kingdom 
that they do not yet give a basis for broad generalizations. 
Very little is known of the earlier stages in the formation 
of hosts of insects whose later metamorphoses, including 
the change of the already advanced larva, first to the con- 
dition of a chrysalis and then to that of a perfect insect, 
have been carefully traced. It remains to be ascertained 
to what extent the caterpillars of different kinds of butter- 
flies, for instance, resemble one another during the time of 
their formation in the egg. An immense field of observa- 
tion is open in this order alone. 
" I have, myself, examined over one hundred species 
of bird embryos, now put up in the museum of Cambridge, 
and found that, at a certain age, they all have bills, wings, 
legs, feet, <fcc., <fcc. exactly alike. The young robin and 
the young crow are web-footed, as well as the duck. It is 
only later that the fingers of the foot become distinct. 
How very interesting it will be to continue this investiga- 
tion among the tropical birds ! to see whether, for instance, 
the- toucan, with its gigantic bill, has, at a certain age, a 
bill like that of all other birds ; whether the spoonbill ibis 
has, at the same age, nothing characteristic in the shape 
of its bill. No living naturalist could now tell you one 
word about all this ; neither could he give you any infor- 
mation about corresponding facts in the growth of the 
fishes, reptiles, or quadrupeds of Brazil, not one of the 
young of these animals having ever been compared with 
the adult. In these lectures I only aim at showing you 
what an extensive and interesting field of investigation 
opens before us ; if we succeed in cultivating even a few 
corners of it we shall be fortunate." 
