40 PROFESSOR DUNS ON THE 



orgauisms, the mature organisms tliemselv^s^ the countless 

 adaptations between different but inter-dependent parts of 

 animal structure, between the organs of animals and their 

 habits, and also between individual forms and their environ- 

 ments. An unresting metabolism pervades all animated 

 being. There is nothing stable, nothing sure. Biological 

 data warrant a doctrine of teleology, changeful, however, as the 

 data themselves, and this is held to supersede the hitherto 

 widely-accepted doctrine of design. According to the other 

 view, the tendency to vary is recognised, but it can work only 

 within sharply- defined limits. It can influence specific 

 features, but we have no proof that it has ever obliterated 

 them, either by the action of incident extei^nal forces or by 

 inherent energy of any sort. On the contrary, it can be 

 shown that the facts both of palseontology and of the life 

 history of recent forms make this in the highest degree im- 

 probable. It is granted by all that the adaptive principle 

 may find as full expression in the growth stages of an animal 

 as in the adjustment and subordination of organs among 

 themselves, or in their relations to the functions for which 

 they exist. Now, avoiding the term '^ species,^^ and using 

 ''individual" instead, the persistence of a zoological class 

 depends on the continuance of identical grooves for the 

 development and succession of the individuals which make it 

 up. This is implied in the reproduction of distinct indi- 

 viduals. But there is not only a definitely-charactei'ised 

 starting-point; there is also development along lines which 

 every palaeontologist knows have not changed throughout 

 gi-eat ages. Students of recent Crustacea acknowledge their 

 indebtedness to paleeontology for help in making out the 

 immature stages of the king crabs {Limulus)' and other 

 genera. Barrande has shown that one trilobite of lower 

 Silurian age {Triniicleus ornatus) passed through six stages 

 from egg to maturity ; another [Sao liirsuia) seventeen; and 

 another {Arethusina honink't) twenty-two. We have thus (1) 

 proof of the existence in earliest Silurian time of a group of 

 crustaceans as high in structural rank as their present repre- 

 sentatives, and whose embryonic development corresponded with 

 theirs; (2) we have evidence that the metabolism with which 

 present allied forms are credited does not so influence them 

 as to alter the grooves within which development takes place. 

 It is inconceivable that, necessarily, random natural selection 

 could ever have determined these stages of growth, or have 

 brought about and rendered persistent the complex sei'ies of 

 fitnesses associated with them ; the more so that the Darwinian 



