CLASSIFICATION OF ANIMALS. 



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The mouth opens in a direction j^arallel with the axis of the bodj% 

 is provided with two jaws, placed one above or in front of the other. 

 The blood is I'ed. 



The heart is a compact muscidar organ, 

 having never fewer than two cavities, an au- 

 ricle and ventricle. 



The muscles surround the bony or gristly 

 levers on which they act, or, in other words, 

 the skeleton is internal. 



The locomotive membei's never exceed two 

 pairs. 



The sexes are distinct. 

 In the sub-kingdom Mollusca, or Hetero- 

 gangliata, the principal centre of the nervous 

 system bears the form of a ring, surrounding the gullet, from which 

 the nerves radiate, often unsymraetrically, to different 

 parts of the body {fig- 2.) : the brain is represented by 

 ganglions above (a) or at the side (b) and below the gullet; 

 other ganglions (c d) are developed in other parts of the 

 body. The form of the body corresponds with the dis- 

 position of the nervous system, and is commonly unsym- 

 metrical. In a single order (^Cephalopods) the muscles 

 originate from an internal rudimental cartilaginous skele- 

 ton : in the rest they are attached only to the skin, which 

 forms a soft envelope in which there are developed in 

 many species one or two calcareous plates, called shells. 



The blood is colourless, or not red ; the heart compact, 

 muscular, and propelling the blood through a closed sys- 

 tem of arteries and veins. 



The respiratory organ is never wanting ; and, with the 

 exception of one family (Ascidiatis), the cavity contain- 

 ing it communicates with or opens near the anus. 

 The Mollusca are dioecious or hermaphrodite. 

 The third primary division of the animal kingdom, viz. 

 the Articulata, has the brain in the form of a ring, em- 

 bracing the gullet : a double ganglion above the tube 

 supplies the organs of sense : from the sub -oesophageal 

 ganglions two chords are extended along the ventral sur- 

 face of the abdomen, and are, in most species, united at 

 certain distances by double ganglions, which give origin 

 to the nerves of the extremities {Jig. 3.). From the sym- 

 metrical disposition of the nervous centres, I have called 

 this sub-kingdom Homogangliata. The body presents a 



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