152 THE DOCTRINE OF DESCENT. 
where, has opposed to the ‘Divergence of Character, ot 
the inclination of varieties and species to deviate from 
one another, a Convergence of Character. It is con- 
ceivable, he thinks, that species derived from different 
genera, might sometimes approach each other so 
closely that they would be classed in the same 
genus. The author of the theory of Selection has been 
content to point out the great improbability of such an 
event, which, moreover, in this simplicity would scarcely 
impugn the origin and truth of the theory. “If two 
species of two allied genera both produced a number of 
new and divergent species, I can believe that they might 
sometimes approach each other so closely that they 
would, for convenience’ sake, be classed in the same.new 
genus, and thus two genera would converge into one; 
but from the strength of the principle of inheritance, 
and from the two parent species already differing, and 
consequently tending to vary in a somewhat different 
manner, it seems hardly credible that the two new 
groups would not at least form different sections in the 
same genus.” * 
We here see a theoretical objection theoretically 
refuted. But although the probability of a convergence 
carried to absolute similarity is.extremely slight, and 
it receives no support from the paleontological record, its 
utter @ prior? impossibility must not be rashly asserted ; 
and in my researches on the Sponges of the Atlantic, I 
have pointed out groups of species approximating so 
closely as to be scarcely distinguishable. Chalina and 
Reniera are two distinct genera, actually belonging to 
different families. It is highly probable that the genus 
Chalinula, with its extremely variable species, are 
