I A CHAPTER IN DARWINISM 35 



gree to which fishes, reptiles, birds, beasts, and men 

 belong. And the combination of these marks or 

 structural peculiarities is an overwhelming piece of 

 evidence in favour of the suj^position that the creatures 

 which possess this combination are derived from one 

 common ancestor. Just as one would conclude that a 

 man whom one might meet, say on Salisbury Plain, 

 must belong to the New Zealand race, if it were found 

 not only that he had the colour, and the hair, and the 

 shape of head of a New Zealander, but also that he 



SPINAL CHORD 



NOTOCHORD 



POSITION OE SPIRACLE CILLSLITSI; 



SPINAL CHORD / ,g„^,^ „o.j^„ 



^^^ 



NOlOCHORO 



CILL SLhS 



Fig. 17.— Tadpole of Frog and of Ascidian. Diagrams representing -the chief 

 internal organs, 



was tattooed like a New Zealander, carried the weapons 

 of a New Zealander, and, over and above, in addition 

 to these proofs, that he talked the Maori language and 

 none other ; so here, in the case of the vertebrate race, 

 there are certain qualities and possessions, the accumu- 

 lation of which cannot be conceived of as occurrino- 

 in any animal but one belonging to that race. These 

 four great structural features are — first, the primitive 

 backbone or notochord ; second, the throat perforated 

 by gill-slits ; third, the tubular nerve-centre or spinal 

 cord and brain placed along the back ; and lastly, and 



