METAZOA. 



11 



Grade B. METAZOA (Enterozoa). 



The unicellular Protozoa are contrasted with the remaining animals 

 forming Grade B METAZOA, which possess cellular differentiated 

 tissues and organs. Sexual reproduction by ova and spermatozoa. From 

 the fertilized ovum a Blastula is produced by continued cell-division 

 (cleavage), and from this a Gastrula with Ectoderm and Endoderm. 



The probable phylogenetic connection of the Metazoan classes is shown 

 in the following scheme ; and several important typical differences are 

 collected together in the annexed table : 



Mammalia ^ 



Aves g 



Reptilia $ 



Amphibia 

 Pisces Cyclostomi 



Cephalochorda 



Cephalopoda Pteropoda 



Hemichorda 



Gastropoda 

 to | 



?> Lamellibranchiata 



Molluscoidea \ 



Insecta 

 Myriapoda 

 Urochorda Protracheata 



Nemertea 



Cestoda Mesozoa 



V 



Trematoda- 



Arachnida 



Crustacea 



/ 

 Annelida 



Holothuroidea 

 Echinoidea 

 Asteroidea 

 Criuoidea 



Acanthoc 



Nematoda 



irbellaria 

 Ctenophora 

 Spongise Cnidaria 



Ccelenterata 



Cell Colonies 



Protozoa 



