OUTLINES OF THE ANIMAL KINGDOM. 103 



Cuvierian Arrangement. 



1. VERTEBRATA. 



Mammalia. 



Aves. 



Eeptilia. 



Pisces. 



2. MOLLUSCA. 3. ARTICULATA. 



Cephalopoda. 



Pteropoda. Insecta. 



Gasteropoda. Arachnida. 



. 

 Cirrhopoda, Annelida. 



4. E ADI AT A. 



Echinodermata. 



Intestina. 



Acalepha. 



Polypi. 



Infusoria. 



The preceding table is so arranged as to show at a glance the four Cuvierian 

 subkingdoms and their respective classes. The Radiate subkingdom is now 

 scattered. As regards the classes, the names printed in italics indicate those 

 which have been since subjected to various degrees of change, either having 

 received additions, been broken up into distinct classes, transferred to others 

 already existing, or even placed in entirely new subkingdoms. 



The primary divisions or subkingdoms of Cuvier are not founded on any 

 one common principle, but each is based upon a separate mode of distinction 

 or definition. Thus the Vertebrate subkingdom, including, as seen above, the 

 classes of Mammals, Birds, Reptiles, and Fishes, has for its basis a point of 

 internal structure, viz., the possession of a vertebral column or back-bone, 

 forming the fundamental part of the internal skeleton. The subkingdom 

 Mollusca contains the classes Cephalopoda, illustrated by the cuttle-fishes and 

 nautilus ; Pteropoda, or sea-butterflies, marine animals, represented by the 

 clio and others ; Gasteropoda, consisting of snails, slugs, whelks, periwinkles, 

 limpets, and other marine animals with univalved shells, as well as numerous 

 sea-slugs and other allied shell-less species ; the class Acephala, or headless 

 molluscs, including the Testaceous bivalved oysters, mussels, cockles, scal- 

 lops, and others, with the so-called simple and compound Tunicated marine 

 animals ; the Brachiopods, also bivalved marine animals ; and lastly, the 

 Cirrhopods or barnacles. The Mollusca are so named from an external gen- 

 eral character which is common to them all, though less marked in the barna- 

 cles, viz., a soft fleshy kind of body. The Articulate subkingdom comprehends 

 Insecta, with the myriopods, or centipedes, and millipedes ; Arachnida, or 

 spiders ; Crustacea, including crabs, lobsters, shrimps, and many smaller 

 crustaceans ; and all the Annelida, such as worms and leeches. It is based 

 also on a general external character, viz., the more or less jointed or divided 

 form of the body and limbs where these exist. Lastly, the Radiate subking- 

 dom is founded also on an external character, derived from the general radi- 

 ated form of the body, or of the appendages situated around the mouth or 

 oral aperture of the body-cavity : it includes the Star-fishes, the Intestinal 

 "Worms, the Medusa or sea-nettles, the various Polyp-shaped animals, such 

 as the sea-anemones, the gelatinous polyps resembling the little fresh-water 

 hydra, and also the coral-forming polyps ; and finally the class of Infusorial 

 animalcules, including the Rotiferous or wheel animalcules. 



The definitions of the classes were for the most part, and, indeed, always, so 



