DOCTKINE OF EVOLUTION AND RELATED IDEAS 

 Fig. 251. 



491 



UNGUICULATES 



MODERN BIRDS 



TOOTHED BIROS 



ELASMOBRANCHS 



CEPHALOPODS 

 INSECTS 



ARACHN4DA 



ECHINODERMS 



COELENTERATA 



LAMELLIBRANCHE 



COLONIAL PROTOZOA 

 I 

 SIMPLE PROTOZOA 

 Pig. 35X. A diagram designed to suggest something of the possible relationships of the various 

 groups of animals. The vertical position indicates roughly the relative specialization or progress 

 of the groups. 



Questions on the figure. — Which of the groups seem to be centers from which 

 several types may have sprung? What does this mean? Which phyla do not 

 seem to have others springing from them? What does this mean? What three 

 theories as to the origin of the Chordata are suggested in the figure? 



