94 THE EVOLUnOW OF MAN. 



worm tribe ; but the parent-forms of the three formei 

 belong to worm-groups quite distinct from that of the 

 Chordonia. It is only far down at the common root of the 

 group of Coelomati, that we assume a common source for 

 these various tribal forms. (Cf. Tables XVIII. and XIX.) 

 It is especially necessary to remember that there is no 

 direct blood-relationship between Vertebrates and Articu- 

 lated Animals. 



The Articulated Animals (Arthropoda), to which the 

 most comprehensive of all classes of animals, that of Insects, 

 and also the Spiders, Centipedes, as weU as the Crabs, or 

 Crustaceans, belong, are descendants of articulated Worms, 

 the nearest allies of which are the extant Ringed Worms 

 (Annelida). The tribe of Star-animals (Echinoderma), 

 which includes the Star-fishes, Sea-lilies, Sea-urchins, and 

 Sea-cucumbers, must also have descended from similar articu- 

 lated Worms."^ The parent-form of the Soft-bodied Animals 

 (Mollwsca), which include the Cuttles, Snails, Mussels, and 

 Lamp-shells, must also be sought among the Worms. But 

 the Coelomati, from which these three higher animal tribes 

 originated, differed entirely in character from the Chorda- 

 animals. Unlike the latter, they never developed a noto- 

 ohord. In them, the anterior section of the intestinal tube 

 was never modified into a gill-body with gill-openings; nor 

 were the upper throat-ganglia developed into a medullary 



tube. In a word, in Articulated Animals, Star-animaJs, and 



if 



Soft-bodied Animals, as well as in their ancestors among 

 the Blood-bearing Worms, the typical structural peculiari- 

 ties which are exclusively characteristic of the vertebrate 

 tribe and of their immediate invertebrate progenitors, were 

 never present Thus the great majority of all Miimalfl are 



