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 Linnaeus's ' Sy sterna Naturae ' in 1735, with the four 

 thousand qnarto pages and more than six hundred plates 

 employed by the Challenger Eeports 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,' 

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