1886.] Geological Extinction and some of its Apparent Causes. 29 
tain, the results of domestication as affecting pectoral develop- 
ment is readily seen; 
Ruffed grouse (Bonasa umbellus) 15.51 per cent, 
Hen. A “ 
Wild goose (Branta canadensis) $ 10.22 w 
OME a A E T a e 6.40 “ 
I do not claim that from this list the exact place of a bird can 
be given as to its power of flight, because other elements than 
the size of the pectoral muscles enter into this complex problem 
so as to preclude an absolute classification on the basis of pec- 
toral development, yet I think that there is a relative variation 
expressed by the figures given in this list, and that when together 
with this element the other elements of flight are considered we 
can tell the place a bird should occupy in the scale of flight. 
"2°. 
VY 
GEOLOGICAL EXTINCTION AND SOME OF ITS 
APPARENT CAUSES 
BY A. S. PACKARD. 
N his Origin of Species, Darwin says: “ The extinction of species 
has been involved in the most gratuitous mystery. Some 
authors have even supposed that, as the individual has a definite 
length of life, so have species a definite duration. No one can 
have marveled more than I have done at the extinction of spe- » 
cies.” Finally, he remarks, “ Thus, as it seems to me, the man- 
ner in which single species and whole groups of species become 
extinct accords wells with the theory of natural selection. We 
need not marvel at extinction; if we must marvel, let it be at our 
Own presumption in imagining fora moment that we understand 
the many complex contingencies, on which the existence of each 
species depends. If we forget, for an instant, that each species 
tends to increase inordinately, and that some check is always in 
action, yet seldom perceived by us, the whole economy of nature 
will be utterly obscured. Whenever we can precisely say why 
this species is more abundant in individuals than that; why this 
species and not another can be naturalized ina given country ; 
then, and not till then, we may justly feel surprised why we 
cannot account for the extinction of any particular species or any 
group of species.” 
The fact of extinction is indeed not less marvelous than that 
f 
