42 Dr Gaskell, The Origin of Vertebrates. [Dec. 2, 



the primitive coelom which is reduced almost to extinction in 

 the adult ancestor ; (viii) that cilia which are primitive have been 

 lost in the ancestor and re-acquired in the descendant, whilst the 

 chitinous coating of the former leaves no trace ; (ix) that the 

 heart has disappeared ; (x) that with the exception of a part of 

 the branchial skeleton, the entire skeleton including the notochord 

 is a new formation, and so are the kidneys and the generative 

 organs; the paper before us throws no light upon the question 

 as to their origin. 



Mr E. J. Bles said that the gap between an Arthropod 

 ancestor and the vertebrates is as great as the gap between the 

 vertebrates and an}^ other ancestral form hitherto put forward. 

 In considering Dr Gaskell's theory it is therefore necessary to 

 make sure that besides deriving support from resemblances in 

 anatomy and histology, the theory takes into account the main 

 distinctions between the hypothetical ancestor and the verte- 

 brates. Using a table from the most recent authority (Haeckel, 

 Systematische Phylogenie der Wirbelthiere, p. 12), it appears that 

 all the valid distinctions drawn between Articulata and Vertebrata 

 have been dealt with in Dr Gaskell's paper. As for the remaining 

 points : (1) the presence of a cuticular layer in vertebrates has 

 been recognised by Leydig, F. E. Schultze, etc., and demonstrated 

 to be chitinous by G. Wolff; (2) the structure and mode of deve- 

 lopment of the notochord throughout the chordates is so uniform 

 that no distinct clue is given to its origin from any pre-existing 

 organ in an ancestral form. 



Dr Gaskell said in reply — I have listened most carefully 

 to the arguments brought forward against my theory, and it 

 seems to me that the most important of them may be summed up 

 as follows. 



"The resemblances and coincidences between the structure of 

 Ammocoetes on the one hand and of Limulus and Scorpions on 

 the other which I have brought forward are mere trivialities in com- 

 parison with the true criteria of what constitutes a Vertebrate, viz. 

 the presence of a coelom of a more primitive type than that of an 

 Arthropod, and the existence of a notochord. These are the two 

 most important points, and as I have given no explanation of 

 them, the coincidences which I have pointed out, although inter- 

 esting, are of no real importance." 



I quite understand that these close resemblances between 

 similar parts in Limulus and Scorpions and in Ammocoetes are 

 very unorthodox, but thej^ are certainly not trivial. The argument 

 reminds me of the commotion made in the orthodox world when 

 it was first suggested that man and the ape were closely akin ; 



