APPENDICULATES AND VERTEBRATES 81 



to the external configuration of the body, and 

 some of them at least are sufficiently remark- 

 able, not to say astonishing. Perhaps one of 

 the closest degrees of functional convergence is 

 that which is manifested between the appendi- 

 culate (annelid and arthropod) and vertebrate 

 central nervous systems, upon which attention 

 has been focussed by Dr Gaskell. The central 

 nervous apparatus is the dominant system in 

 the organisation of the higher animals, and he 

 thinks that it has been a dominant factor in 

 evolution. The comparison tabulated below from 

 Dr Gaskell's recently published volume on the 

 "Origin of Vertebrates "( London, 1908) appears 

 to me to serve as a most beautiful example of 

 true physiological convergence, but likely to be 

 confounded with the spurious convergence pre- 

 sented by the so-called cephalic stomach of the 

 arthropod in comparison with the ventricles of 

 the brain in the craniate vertebrates. Now, it 

 may appear something like an impertinence to 

 describe as a spurious convergence what Dr 

 Gaskell regards as a true homology ; it is, how- 

 ever, nothing of the kind, and is no more than 

 an expression of the opposite point of view. On 

 that understanding we may leave it for the 

 present, perhaps returning to it later, either 

 directly or by implication. 



