830 The American Naturalist. [October, 
breathing both by its lungs and by taking water into its mouth. 
A still more striking example is given by Prof. Cope. The 
young Siren almost entirely loses its gills and later regains 
them, becoming again almost as completely aquatic in its 
habits as in the larval stage. 
With these examples which may be seen by any one each 
recurring year, is it impossible or difficult to conceive that in 
the struggle for existence the soft-shelled turtles found the 
searcity of food, the dangers and hardships of the land, greater 
than those in the water? On remaining constantly in the 
water, and advantageously submerged for most of the time, 
it gradually reacquired the power of making use of its phar- 
ingeal membrane for obtaining oxygen from the water and 
excreting carbon dioxide into it as had its remote ancestors. 
And further, is it not intelligible that with capacious lungs, 
which it can fill at intervals with air containing so largea 
supply of oxygen that it, like the other double or mixed 
breathers, should use its lungs to supply most of the oxygen 
and its throat to get rid of much of the carbon dioxide? 
Indeed, it seems to me that if the evolution doctrine is a 
true expression of the mode of creation, then development 
may be in any direction that proves advantageous to an organ- 
ism, even if the development is a re-acquirement of long dis- 
carded structures and functions (11). 
- Ñn closing may I be permitted to say to the older biologists, 
to those familiar with the encouragements and inspirations 
that come with original investigation, that I trust they will 
pardon what to them is unnecessary personality or excess of 
detail in this address for the sake of the younger ones among 
us, to whom the up-hill road of research is less familiar. 
Judging from my own experience in listening to similar 
addresses by my honored predecessors, it is helpful to know, — 
when one is beginning, something of the “dead work,” the 
difficulties and discouragements as well as the triumphs in 
the advancement of science. 
REFERENCES. 
1. Milne, Edwards.—Lecgons sur la Physiologie et l’ Anatomie 
Comparée de Homme et des Animaux. Tome i, Paris, 1857. 
