THE NEW GENEALOGICAL TREE 



463 



Chordata 



Arthropoda 

 MoUusca I .Annelida 



Hemichordata 

 Echinodermata 



Other 

 Sch/zocoela 



Echiuroidea 



Nemertina 

 Trochophore / 



// Platyhelminthes 



^^^^^^ 



? ? 



Primitive acbel f'latworms 

 I 



BILATER/A 



Asctielminthes 



Ctenophora 

 Cnidaria 



Planula 



Porifera 



Primitive medusa 

 l^esozoa 



Ottier Protozoa 



riagellata 



Fig. 61. Evolutionary relationships of the animal kingdom. (After 

 Hyman.) 



hand my own system. At first sight the differences be- 

 tween these two systems appear to be very great. We will 

 now try to show that these differences are not actually quite 

 so great, and that they can easily be overcome if only we 

 have a little tolerance and good will. I will therefore enumerate 

 here all those changes which can help us to overcome these 

 differences. Such changes are actually not quite so numerous. 

 In order to solve first major problems we must abandon 

 above all the two large groups of the Bilateria and Radiata ; 

 all the Eumetazoa are actually bilaterally symmetric animals, 

 and there remain the Cnidaria and the Ctenophora only as 

 members of the Radiata. The Echinodermata are quite cor- 

 rectly excluded from this group; there are few purely radially 



