DOCTRINE OF EVOLUTION AND RELATED IDEAS 



485 



FIG. 251. 



UNGULATES 



UNGUICULATES 



MODERN BIRDS 



CURSORES 



TOOTHED BIRDS 



PLACENTA LS 



MARSUPIALS 

 \ 



MONOTREMES 

 \ 



MODERN REPTILES 



\ 



ARCHAEOPTERYX 



CYCLOSTOMES 



ELASMOBRANCHS 



CEPHALOPOOS 



INSECTS 



ARACHNIDA 



PRIMITIVE CHORDATES 



IXH 



ECHINODERMS 



N. 



COELENTERATA 



GASTEROPODS 



LAMELLIBRANCHS 



PORIFERA 



UNSEGMENTED WORMS 



DIPLOBLASTIC METAZOA 



COLONIAL PROTOZOA 



! 



SIMPLE PROTOZOA 



PIG. 251. 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 Chorda ta are suggested in the figure? 



