GASTRULATION OF THE VERTEBRATES. 417 
This position as a central and archaic form in Vertebrate 
phylogeny, confirmed as it seemed by embryology, is decidedly 
a usurped position, 
gz Oe 
ow 
wruvere 
ae 
Te 
oe 
-° 0 
SI Do 
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o, 
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2° Ky) (} (] 
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Fic. 7.— Earliest stages of cephalogenesis (K) and notogenesis (N) in longi- 
: tudinal median sections. a, Elasmobranchs (Torpedo, after Riickert). 
_ band ¢ Cyclostomes (after Gotte), two successive stages of Petromyzon. 
d, Mammals (Tarsius). ‘Akad. v. Wetensch,,’ Amsterdam, vol. viii, 
No. 6, 1902. 
For as soon as we also consider the anatomy of Amphioxus 
