28 RELICS OF PRIMEVAL LIFE 



to be somewhat unreasonable in demands of this 

 kind, for any cause capable of originating a new 

 form of living being, might have been operative at 

 the same time in different localities and under some- 

 what diverse conditions, and may also have acted 

 at different times. All imaginary lines of descent 

 of animals are more or less subject to this con- 

 tingency ; and this may partly account for the 

 great diversity in the lines of affiliation presented 

 to us by evolutionists, which may in part have a 

 basis in fact in so far as distinct varietal and 

 racial forms are concerned, but may just as likely 

 be entirely fallacious in the case of true species. 

 In any case, in the lowest rocks into which we can 

 trace Crustacea, we have already probably five of 

 the orders into which their successors in the modern 

 seas are divided by zoologists ; and this is certainly 

 a singular and suggestive fact, the significance of 

 which we shall be better prepared to understand 

 at a later stage of our investigation. 



Allied in some respects to the Crustacea, though 

 much lower in grade, are the marine Worms — a 

 great and varied host — usually inhabiting the shal- 

 lower parts of the ocean ; though the 330 species 

 collected by the Challenger expedition show that 



