9 



sometimes called Mn/dcazooids because, like the mol- 

 luscs, their hard part-< are of car})onate of lime. In 

 like manner the Infusorian-; sugg-est the Articulates, 

 and are known as EutoDiozouids. 



The Polycystines connect with their neighbors the 

 Rhizopods ; and in the same way the Sponges connect 

 with the Infusorians, thus completing the coil of ascent, 

 as the Infusorians are, clearly, the most highly organ- 

 ized of Protozoans. 



The Protozoans appeared enrliest in Time, the old- 

 est of known fossils beiui^- Eozoon. belono'inu" to the 

 rocks of the Pre-Cambrian Period. 



From the Protozoans arise a central stem of Meta- 

 zoAXs, of which the branches lowest in structure are 

 the C(ELEXTKHATA ( Conds aud Allies), iind the Eciii- 

 NODERMATA ( Star-Fislies, c^c. ) This pair of branches 

 constitute the '• Radiata," although the Echinoderms 

 and even the higher (Juelenterates manifest a degree 

 of bi-laterality. 



The succeeding pair of branches in this inverte))rate 

 circle, are the Molli:s("a and Artki^lata. Of these 

 Agassiz remarks,"' We cannot i)redicate absolute superi- 

 ority or inferiority of organization of either group as 

 compared with the other ; they stand on one structu- 

 ral level, though with different tendencies." This is 

 entirely consistent with the idea that they are oppo- 

 site and complementary members of one pair, in a 

 system of dichotomous Ijranching. 



The Coelente rates (through the Polyps) connect so 

 closely with the Sponges below them that the best 

 palieontologists hesitate to say of certain ancient forms 

 whether they are sponges or (*(^i-al. 



