DOES ADVANTAGE IN UNIFORMITY EXPLAIN DIVERGENCE? 261 
right-handedness, there is a distinct advantage in uniformity, and that consideration 
alone may perhaps suffice to explain Mr. Gulick’s difficulty. Among plants it 
may seem less obvious, but where seedlings are crowded, uniformity may save 
space, just as a number of objects of the same shape can usually be packed into 
less space than those of diverse shapes. More plants can grow in a window-box 
when all bend to the light than would be possible if half of them bent one way 
and half another. 
There also occurs to me a theoretical consideration, perhaps of doubtful value. 
When a germ has diverse potentialities, so that it is left to germinal or environ- 
mental selection to decide which course it shall take in development, there must 
apparently be a certain waste of germinalenergy. Any disadvantage thus arising 
is ordinarily much more than counterbalanced by the gain due to the adapta- 
bility of the organism, or in social species to the power of specialization of the in- 
dividual for social purposes. But it may be that when no such advantage is 
found, there exists a small disadvantage in deviations, potential or axial, froma 
common standard. 
What we really need, in discussing these matters, is the observation of actual 
facts. The facts above related as to Campeloma are worth more than any amount 
of theoretical considerations. 
T. D. A. CocKERELL. 
MEsILLA, NEw Mexico, U.S. A., April 21, 1897. 
6. Reply to Letter of T. D. A. Cockerell. 
The advantage in uniformity is very manifest in certain cases; and, on pages 
68-70 of this volume, I refer to conditions in which it is more manifest than in 
the cases here suggested by Mr. Cockerell; but the advantage of uniformity 
does not ‘‘explain the difficulty’”’ I have raised. For how can the advantage 
of uniformity explain the introduction of permanent diversity through the sur- 
vival of a variation that breaks down the former uniformity, and establishes two 
forms where there was a single form? 
The disadvantage in deviation from a common standard, if it can be shown to 
be a fact, is perhaps akin to the fact that variations most widely diverging from 
the average form are usually less fertile. But how can the advantage of a com- 
mon standard cause the dividing of a species according to two different standards 
as in the case of some snails? For any one snail of a dextral group there may be a 
disadvantage in being of a sinistral form; but does that throw any light on why a 
species should, under one environment, divide itself into two groups, one being 
dextral and the other sinistral? and does it show that the process is due to nat- 
ural selection? The best explanation I can suggest is given on pages 68-7o. 
J. TAGULick, 
