CRITIQUE OF DARWINISM 257 
placed a number of crabs in a large aquarium, in which china-clay was 
kept partly in suspension, and found that about half of them died. 
Again the survivors were compared statistically with the perished and 
the same relation was found to hold: that the survivors had a mean 
frontal breadth distinctly narrower than that of the perished. Wel- 
don concludes that his experiments “have demonstrated two facts 
about these crabs; the first that their mean frontal breadth is dimin- 
ishing year by year at a measurable rate, which is more rapid in males 
than in females; the second is that this diminution in frontal breadth 
occurs in the presence of a material, namely, fine mud, which is 
increasing in amount, and which can be shown experimentally to 
destroy broad-fronted crabs at a greater rate than crabs with narrower 
frontal margins ....and I see no escape from the conclusion 
that we have here a case of Natural Selection acting with great 
rapidity, because of the rapidity with which the conditions of life 
are changing.” 
Cesnola’s experiments with Mantis.—To test the selective value 
of color markings Cesnola fixed specimens of the brown and green 
Mantis religiosa on plants, some of which were against harmonious, 
others against disharmonious backgrounds. The result was that most 
of those which were inconspicuous because of a harmonious back- 
ground escaped, while most of the others were eaten up by birds. 
Poulton’s and Sanders’ experiments with butterfly pupae.— 
Numerous pupae of various colors were placed under conditions favor- 
ing protective coloration and others under opposite conditions. The 
conclusion was that protective coloration is a real survival factor, and 
one that operates so as to give the protectively colored individual 
a decided advantage in the struggle for existence. 
Davenport’s experiments with chickens.—A number of chickens, 
some black, some white, and some barred or checkered in color, were 
allowed to wander free in the fields. Hawks killed most of the whites 
and many of the blacks, but spared, to a large extent, the less con- 
spicuous checkered and barred types which are harder to detect 
against a mixed background. 
All of these experiments merely tend to show that discriminate 
survival actually occurs, but only the experiment of Weldon has a 
bearing on the possibility that mere quantitative changes of small 
dimensions might under certain conditions be of selective value. We 
badly need more experimental evidence of this sort and until this 
is forthcoming we shall have to admit that there is very little 
