Chap. IX. 
MOLLUSCS AND ANNELIDS. 
327 
dark recesses. So that with these nudibranch molluscs, 
colour apparently does not stand in any close relation 
to the nature of the places which they inhabit. 
These naked sea-slug3 are hermaphrodites, yet they 
pair together, as do laud-snails, many of which have 
extremely pretty shells. It is conceivable that two 
hermaphrodites, attracted by each others greater beauty, 
might unite and leave offspring which would inherit 
their parents’ greater beauty. l>ut with such lowly- 
organised creatures this is extremely improbable. Nor 
is it at all obvious how the offspring from the more 
beautiful pairs of hermaphrodites would have any ad- 
vantage, so as to increase in numbers, over the offspring 
of the° less beautiful, unless indeed vigour and beauty 
generally coincided. We have not here a number ot 
males becoming mature before the females, and the 
more beautiful ones selected by the more vigorous 
females. If, indeed, brilliant colours ivere beneficial 
to an hermaphrodite animal in relation to its general 
habits of life, the more brightly-tinted individuals would 
succeed best and would increase in number ; but this 
Would be a case of natural and not of sexual selection. 
Sub-kingdom of the Vermes : Class, Annelida (or Sea- 
loorms ). — In this class, although the sexes (when separate) 
sometimes differ from each other in characters ol such 
importance that they have been placed under distinct 
genera or even families, yet the differences do not 
seem of the kind which can be safely attributed to 
sexual selection. These animals, like those in the pre- 
ceding classes, apparently stand too low in the scale, 
f, m the individuals of either sex to exert any choice in 
selecting a partner, or for the individuals of the same 
Sl x to struggle together in rivalry. 
