JO 



The Mollusca, on one side connect with the Coelen- 

 terates, throngh the branches known as Molhiseoidea, 

 and especially by the Polyzoa ; and on the other side 

 the Cephalopods rest npon an Echinodennatons base. 



The Worms by their lowest branch, the Rot if era ^ 

 tonch npon the Infusoria ; they also through other 

 forms connect with ancient Echinoderms, while by 

 their complete circulation the highest l)ranch, the 

 Anit€H(Ja, approaches the vertebrates. 



Molluscan and Articulate forms sometimes resemble 

 each other so closely that it has required the most 

 profound research to distinguish lietween the two. 



All four of these invertebrate branches diverge from 

 a connnon stem : hence these resemblances to each 

 other, and to their Prott)zoan stock. 



The Articulates appeared in the Lower Cambrian ; — 

 in America, with the genus Par ado. mules. The lower 

 Molluscs and Radiates foUowed during the deposition 

 of rocks of the Camljrian and Lower Silurian Periods, 

 bnt it was not nntil later, at the base of the Upper 

 Silurian, that the Cephalopods entered upon existence. 



With the Upper Silurian, the Vertebratp: Stem 

 budded from the invertebrate base. 



Some of the earliest vertebrates of the family Ceph- 

 alaspklxe remind us cnriously of l)Oth the Trilobites 

 and the Orfhoceratidce, — that is, of both Articidate and 

 Molluscan forms. 



The vertebrate which is lowest in structure, but 

 which belongs to a later period, appears to have taken 

 its rise from the opposite side and to be derived from 

 the Coelenterates and lower MoUuscans. 



All molluscs, articulates, and vertel)rates are bilateral 



