206 



ZOOLOGY 



This is believed to be the forerunner of the appendages of 

 vertebrates. 



This review of the most primitive chordates indicates that 

 the ancestors of vertebrates were elongated, worm-like, seg- 



Tatpl M 

 — ^ alrp -venlfr 



mj/om ^orsfr 



dors^ 



'^^''''^MWM¥^^ 



zSMfm^ W^!^^^^&^ 



' or.hd 



lenl^r 



"4/ 



j/OT> ml pi V 



Fig. 280. — Amphioxus lanccolatiis. A, ventral ; B. side view of the entire 

 animal. nn, anus; atrp, atriopore ; cd.f, c-audal fin: cir, cirri; dors.f, 

 dor.sal fin; dors.f.r, dorsal fin-rays; oon, gonads; tiifpl, nietaplcure ; 

 myoni, myomeres; nch, notochord ; or.hd, oral hood; vent.f, ^•ent^al fin; 

 reni.f.r, ventral fin-rays. After Kirlvaldy. 



mentcd animals. In this respect they resembled annelids, 

 but in certain respects the internal organs of vertebrates are 

 inverted as compared wnth those of invertebrates thus : — 



It will be seen that the relations of the above j^arts in verte- 

 brates become the same as in Invertebrates if we think of the 

 former as turned on their backs. It seems, at first sight, 



