263 
ZOOLOGICAL LITERATURE. 
hensively as possible tlieir common origin, might give one of 
the three following results 
1. Darwin's propositions, if incorrect, might lead, by their 
application, to irreconcileable and contradictory conclu- 
sions, which accumulating would demonstrate their error 
with a certainty equal to mathematical proof. 
2. That the experiment might succeed in a more extended 
or more limited manner, were it possible to show, by 
the help of Darwin's doctrine, in what succession the 
various more or less extended circles separated from the 
common type and from each other, and in what succes- 
sion they had acquired their now distinct peculiarities. 
« Were it possible to obtain such a genealogical history 
of any one group of animals, the more completely this 
exposition included . the known species, and the deeper 
research it made into individual forms, so much the more 
obvious would it make the truth, and afford convincing 
evidence that the theory was something more than an 
imaginary dream. 
3. Certainly it is possible, and even most probable, that 
the experiment might fail, from the difficulties to be sur- 
mounted, without deciding the question. Should it how- 
ever succeed, it would, from its independent and perfect . 
character, be considered evidence of real value." 
Having determined to put the experiment to the test, he 
fixed upon the class Crustacea as being the one most likely to 
afford him the fullest opportunity, — first, because there is no 
class of animals in which the differentiation is so great or diver- 
sified, passing as they do from the planaria-like form of the 
female of the parasitic -CryptoniscuSi at the one extreme, to that 
of the macrurous Decapods at the other; and secondly, be- 
cause the shores of the South Atlantic offered to him at Desterro 
the greatest amount of the most varied forms, affording species 
of every group except those of Phyllopoda and Xyphosura. 
Before all things, a perfect acquaintance with the develop- 
ment of each individual form is essential; and much as has 
beeii done of late, it only affords evidence of how defective is our 
knowledge in this respect ; for the new forms that have been found 
to exist in the larval stage of many species are so many argu- 
ments demonstrating the necessity of a closer inspection of the 
earliest stages of yet unexamined species. 
If. In the commencement of this chapter Dr. Muller makes 
the following remark, which appears well worthy of the con- 
sideration of those who are inclined to answer this important 
theory from the imperfect data at our command, That the 
same weight may be counted in favour of Mr. Darwin's theory, 
by the absence of proved contradiction, as his opponents apply 
against him on the absence of proved intermediate forms be- 
tween known species in the different strata of the earth's crust." 
