THE GEOLOGIC FUNCTIONS OF LIFE. 



659 



matter into organic animal matter, and this is sometimes really an 

 advance in organization. The organized animal matter is subject to 

 preservation in some small degree, though it usually perishes. Some 

 contribution is, therefore, made to the organic deposits, chiefly in the 

 form of hydrocarbons. It is the view of some geologists that the natural 

 oils and gases have an animal origin in the main. 



REFERENCE TABLE OF THE PRINCIPAL GROUPS OF ANIMALS.^ 



Protozoa 



(The simplest 

 animals) 



CCELEXTERATA 



(Sponges, corals, 

 jellyfishes) 



ECHIXODERMATA 



(Crinoids, star- 

 fishes, sea-urchins) 



Vermes 

 (TS^orms) 



MOLLUSCOIDEA 



(Mollusc-like forms) 



MOLLUSCA 



(Molluscs) 



Arthropoda 



(The articulates) 



Porifera 

 Cnidaria 



Pelmatozoa 



Asterozoa 

 Echinozoa 



Branchiata 



. Tracheata 



Vertebrata 



Rhizopoda 



Flagellata 



Infusoria 



Gregarina 



Foraminifera. 

 Radiolaria. 



UnknowTi in fossil state. 



Spongise 



After 



j Calcareous sponges. 

 ( Silicious sponges. 

 j Anthozoa, coral polyps. 

 i Hydrozoa, hydroids and medusae. 



Cystoidea, cystids. ^ 



Crinoidea, stone lilies. 



Blastoidea, blastids. 

 i Ophiuroidea, brittle-stars 

 ( Asteroidea, starfishes. 

 i Echinoidea, sea-urchins. 

 ( Holothuroidea, sea-cucumbers. 

 ' Platvhelminthes 1 



Netathelminthes [ Rare as fossil. 

 Gephyrea J 



.\nneiida, sea-worms. 

 J Bryozoa, sea-mosses. 

 Brachiopoda, lamp-shells. 

 Pelecypoda, lamellibranchs, bivalves. 

 Scaphopoda, tusk-shells. 

 Amphineura, chiton. 

 Gastropoda, univalves, snails, etc. 

 . Cephalopoda, nautilus, cuttlefish. 

 ' Crustacea. 



Trilobita, trilobites. 

 Gigantostraca, horse-shoe crabs. 

 Entomostraca, ostracoids, barnacles. 

 Malacostraca, lobsters, crabs. 

 MATiapoda, centipedes. 

 Arachnoidea, spiders, scorpions. 

 Insecta, insects. 

 ' Cyclostomata, lampreys. 



f Selachii , sharks. 

 Holocephali, spook-fishes. 

 Dipnoi, lung-fishes. 

 Teleostomi, ganoids and teleosis. 

 (common fishes). 

 Amphibia, amphibians, batrachians. 

 Reptilia, reptiles, 

 Aves, birds. 



Mammalia ( Prototheria, monotremes. 

 (mammals) ■< Metatheria, marsupials. 

 ( Eutheria, placentals. 



Zittel in the main. 



Pisces 



(fishes) " 



