ZOOLOGY: W. H. LONCLEY 
733 
tribution and more or less evanescent in continuity, to the streams that 
flowed constantly in one direction and eventually into an unnatural 
habitat, the sea. They needed a more direct and quicker embryonic 
development, requiring, it would seem, the abandonment of the nauplius 
stage. It may therefore well be that the trilobites retaining the nauplius 
stage did not give rise to these stocks, as is sometimes assumed. We 
may have to look for this ancestral stock in one still more primitive, 
and the Protocaris-Apus line of branchiopods suggests itself, but what- 
ever the stock, it would seem to have permanently invaded the rivers 
of the land either in Proterozoic time, or that postulated intermediate 
stage in the earth's history previous to the Cambrian but of which we 
have not a trace of direct evidence, the Lipalian time of Walcott. 
IT. C. Chamberlin, Jour. Geology, 8, 400-412 (1900). 
2 J. Barren, Bull. Geol. Soc. America, 27, 345-436 (1916). 
3M. O'Connell, Bull. Buffalo Soc. Nat. Hist., 11, No. 3, 1-277 (1916). 
^ J. M. Clarke and R. Ruedemann, The Eurypterida of New York, Mem. New York 
State Mus., No. 14 (1912). 
OBSERVATIONS UPON TROPICAL FISHES AND INFERENCES 
FROM THEIR ADAPTIVE COLORATION 
By W. H. Longley 
GOUCHER COLLEGE. BALTIMORE 
Received by the Academy, November 24, 1916 
The conception that species have been multiplied by divergent evo- 
lution of related strains is based upon a great body of verifiable obser- 
vations. Sound judgment has not been exercised consistently, how- 
ever, in the attempt to establish the fact that their development has 
been directed throughout by natural selection. 
If the Darwinian hypothesis is true, the characters of organisms should 
be largely of an adaptive sort, but its adherents have failed, upon the 
whole, to distinguish between shadow and substance, and have been 
content to support their position by imputing utility to structures 
and habits, when nothing less than rigorous proof of the fact will suffice. 
It is not demonstrated, for example, that any class of markings serves 
for purposes of recognition, or for signalling between individuals of 
one species. Neither is it proved that some color combinations warn 
off possible enemies, nor, indeed, that any type of pigmentation is 
functionally conspicuous. The last assumption, nevertheless, under- 
lies a series of suggestions whose apparent conformity with its terms 
is held to support the hypothesis of natural selection. 
