290 NATURAL SCIENCE. November. 



Since, however, Dr. Gaskell's arguments have long been before the 

 scientific public, and since his complete address can now be easily 

 obtained and studied, we shall not recapitulate them here. It may, 

 however, be interesting to record some of the objections that were 

 raised in the discussion. 



In the first place, it is interesting to note that, though one or two 

 speakers, such as Dr. Gadow, seemed inclined to support Dr. Gaskell, 

 or at least to demand for him a fair field, still no attempt was made 

 by anyone, except Dr. Gaskell himself, to rebut the arguments brought 

 forward by the other side. 



As for the supposed difficulty in the tubular nature of the verte- 

 brate central nerve-cord, and its lining by non-nervous tissue. Pro- 

 fessor Weldon, comparing the development of the nervous system in 

 worms, pointed out that the nervous tissue arose from the deeper 

 layers of the derm, which were separated from the outside by a layer 

 of non-nervous ectoderm, while, as Mr. Garstang also insisted, the 

 conversion of the invertebrate system into a tubular system was to be 

 traced in the collar of Balanoglossus, an animal which Dr. Gaskell 

 ignored. Professor Minot, on the other hand, reminded us that the 

 nervous system of Vertebrata was not embryonically a tube, but arose 

 in each individual as a solid mass, which became hollowed after- 

 wards; such a solid nervous system is also found in Invertebrata, and 

 there are no grounds for denying the homology. As for the epithelial 

 lining, the nervous system in Invertebrata has a different embryonic 

 origin from the digestive tract, whereas in Vertebrata the lining of 

 the nerve canal has the same embryonic origin as the central nervous 

 system. The infundibulum, too, if it represented a mouth, should be 

 at the end of this tube, whereas it occurs at the base of the ventral 

 zone of the brain at some distance from the end of the supposed tube. 

 The cerebral hemispheres, moreover, are a product of the dorsal zone 

 of the brain, and therefore cannot be the simple homologues of the 

 invertebrate supra-oesophageal ganglion. 



Dr. Gaskell would explain the packing tissue of the Ammocoetes 

 skull as derived from the liver of Limulus. But similar packing tissue 

 is not so rare, for it occurs, as stated by Professor Weldon, surround- 

 ing the alimentary canal, ovaries, and liver of the crustacean Nebalia, 

 and, as Professor Minot pointed out, round the supra-renal capsules 

 of man, though not of rodents. 



We believe that Professor Hickson was right in affirming the 

 agreement of all morphologists that the alimentary canal of the 

 Vertebrata is homologous with that of the Invertebrata. There may 

 be dispute as to the precise ancestor, but as to this fundamental fact 

 there is none. Dr. Gaskell, however, would have us believe that an 

 entirely new alimentary canal was originated by the closing in of the 

 Lhmilus appendages around a cavity on the ventral surface, portions 

 of these appendages forming the vela of the proctoda^um and 

 stomodaeum. These latter, unfortunately for the hypothesis, are 



