1895.] Dr Gaskell, The Origin of Vertebrates. 37 



In the discussion which followed, Mr A. Sedgwick said that : 



The arguments used by Dr Gaskell to prove that Vertebrates 

 are descended from Arthropods might with equal cogency be used 

 to prove the reverse, viz. that Arthropods are descended from 

 Vertebrates ; Arthropods being quite as highly specialised as 

 Vertebrates. Further the facts alleged in support of the conten- 

 tion are of a superficial and unimportant character, and not of 

 a kind to be brought forward or considered until the more 

 important and deep-reaching anatomical differences between the 

 two groups have been reconciled. For instance such important 

 anatomical matters as the condition of the ccelom, of the nephridia, 

 of the relation of the blastopore to the neural surface are not even 

 referred to. Nor is a single embryological fact brought forward 

 in support of the astounding contention that the alimentary canal 

 of the Arthropod has been changed into the central nerve-tube 

 of the Vertebrate. 



It was further pointed out that Dr Gaskell's paper was wanting 

 in that precision and accuracy of statement required in a specu- 

 lative investigation of this kind ; that it showed internal evidence 

 suggesting that he did not fully appreciate the relative importance 

 of anatomical facts, and finally by the use of certain words and 

 expressions in an erroneous and inaccurate sense it seemed to 

 show that. Dr Gaskell was ignorant of some of the most important 

 principles which must underlie all sound and useful phylogenetic 

 speculation. 



Mr MacBride said that Dr Gaskell had brought forward some 

 interesting points in the anatomy of Ammocoetes but that no step 

 in advance had been made in the direction of solving the ques- 

 tion of Vertebrate ancestry. The objections to be urged against 

 Dr Gaskell's theory on this subject were mainly two. 



1. The Vertebrates in the fundamental constitution of some 

 of their most important organs — viz. coelom excretory organs — 

 belonged to a much more primitive grade of evolution than the 

 Arthropods, inasmuch as the same general arrangement was 

 found in the less differentiated members of many quite distinct 

 phyla, viz. Mollusca, Brachiopoda, Polyzoa, Annelida, &c, whereas 

 the arrangement found in Arthropods was highly specialized. 



2. The reasoning Dr Gaskell employed to prove the descent 

 of Vertebrates from Arthropods was illegitimate. In postulating 

 changes which they suppose to have occurred in the history of 

 the race, zoologists confined themselves to those which could be 

 inferred by comparing together animals of undoubted affinity with 

 each other. 



There was no evidence that fundamentally important organs 

 such as the alimentary canal could be lost and redeveloped in 

 another place. 



