CONVERGENCE, 15! 
every manual of comparative anatomy affords testimony 
that the series of vertebrate animals now living, present 
series of development which negative the sudden and 
incomprehensible origination of these organs in an im- 
mediate state of completion. How they appeared in 
yet lower grades than are exhibited in the true fishes 
of the present time we may learn in part from the 
lancelet, and in part we may picture to ourselves from 
the corresponding sensory apparatus of the lower Mol- 
lusca, Articulata, and Annulosa. With reference to the 
objections to his doctrine arising from the arrangements 
of the most perfect organs, Darwin has said that he 
would abandon his whole theory if it can be shown 
that any of these organs could not possibly have been 
formed from lower grades, by improvement slowly ac- 
quired. This demonstration no one has yet undertaken, 
nor will it ever be undertaken with success, as every 
deeper penetration into the comparative anatomy of the 
sensory apparatus affords evidence to the contrary. In 
order to understand the presumptively faultless sensory 
organs and their derivation from a lower grade, it is of 
supreme importance to bear in mind the circumstance 
first exhibited by Helmholtz in the eye, that besides a 
number of perfections, they likewise possess a number 
of imperfections, and purposeless or obstructive arrange- 
ments. 
But we must examine another point, which may 
awaken doubts as to the admissibility of the doctrine 
of Descent, though, strangely enough, it has as yet been 
turned to little account by adversaries, and only inci- 
dentally touched upon by Darwin. In the “Origin of 
Species,” he states, that H. C. Watson, we know not 
