1895.] Dr Gashell, The Origin of Vertebrates. 39 



Monday, December 2, 1895. 



Professor J. J. Thomson, President, in the Chair. 



The discussion of Dr Gaskell's paper " On the Origin of 

 Vertebrates " was resumed. 



Mr H. Gadow said that Dr Gaskell combines the study of 

 physiology with that of morphology, the latter not being restricted 

 to the small branch of ontogenetic research which can be guided 

 only by the method of comparative anatomy. 



Much of the ordnance store of embryologists consists of weapons 

 which are not those of precision, because at present our knowledge 

 of their nature and meaning is far from satisfactory ; for instance 

 notochord, neurenteric canal, nervous system, coelom, metamerism. 

 Objections to Dr Gaskell's hypothesis, which are based upon such 

 features, are very precarious. 



The incredulity, which Dr Gaskell's hypothesis has met with, 

 is referable to two reasons. First, we were ignorant of the 

 astonishing number of important anatomical and physiological 

 features to which Dr Gaskell has drawn our attention in Ammo- 

 coetes and in Limulus, especially the larval Ammocoetes being 

 full of revelations. Secondly, we are prejudiced in favour of one 

 or other hypothetical pedigree of vertebrate descent, although it 

 is not obvious which are at present the favourites, namely Worms, 

 Sea Squirts, Sea Anemones or even Sea Urchins. 



Anyhow, be Dr Gaskell's hypothesis right or wrong, he has 

 stirred up so many morphological questions, which can no longer 

 be neglected, that work has been cut out for us for many years to 

 come. 



Mr Bateson said that it was difficult to make any criticism 

 which should adequately express to the minds of those who were 

 not acquainted with the leading facts of the structure and develop- 

 ment of animals how impossible it was to entertain Dr Gaskell's 

 hypothesis of Vertebrate descent. Several difficulties had already 

 been spoken of, regarding Amphioxus, the Vertebrate Ccelom, 

 the Notochord, &c, any of which seemed sufficient disproof. Two 

 points might perhaps be taken which would make the objections 

 clearer to those who were not professed zoologists. It was natural 

 however that these difficulties should appeal most to those whose 

 zoological studies had taken a wider range. 



First regarding the relation of the nervous systems of Arthro- 

 pods and Vertebrates. Setting apart all phylogenetic speculation 

 it is known by observation that the central nervous system of a 

 Vertebrate separates from ectoderm in the middle line of the 

 dorsal side [of a Vertebrate], that is to say that that nervous system 



