THEN AND NOW 437 
difficult questions of genealogy. On all these lines of 
research knowledge is continually extending. The time 
may be expected to come when, not from any one of them 
by itself, but from all combined, a final system of classifi- 
cation will be established. Apart from all these questions 
the simpler groundwork of the student’s knowledge of 
recent Crustacea will still be incomplete unless the history 
be extended to those other orders mentioned at the outset, 
which comprise forms as varied, as strange, as numerous 
as those of the Malacostraca. 
On the literature of the subject not a little that is 
entertaining might be written. That literature was scanty 
and unfruitful in classical times. At the restoration of 
learning it began, amidst idle tales and inexact observa- 
tions, to lay the solid foundations of science. In the 
present century it has attained an astonishing develop- 
ment, aided no doubt successively by the perfecting of the 
microscope, by the extension of marine research, and by 
an all-pervading desire to arrive at the truth about the 
origin of species. ‘To illustrate the difference between 
what was known of the Crustacea at the beginning of the 
last century and what is known of them at the close of 
the present, one is tempted to contrast the half-dozen 
lines which suffice for the whole class in the first edition 
of Linnzeus’s ‘Systema Nature’ in 1735, with the four 
thousand quarto pages and more than six hundred plates 
employed by the Challenger Reports between 1880 and 
1888 in the discussion and illustration of a host of crusta- 
cean species of which most were previously unknown. 
The ‘System of Nature,’ it is true, began in small com- 
pass, and was repeatedly expanded in successive editions, 
but even in the thirteenth, published in 1788, that part 
of it which may fairly be regarded as a manual of all the 
Crustacea with which science was at that period acquainted, 
is swollen only to the extent of fifty-three octavo pages. 
In 1825 the French writer, A. G. Desmarest, could still 
confine within the limits of a single volume an able 
and meritorious survey of the whole subject, but not 
long afterwards the masterly ‘ History of the Crustacea; 
32 
