CHAP. XIIL] THE CAT'S PLACE IN NATURE. 451 



Let us now revert for a little time to some of the facts we have 

 reviewed as to the cat's structure, selecting certain characters 

 (for reasons which will shortly appear,) and viewing them in the 

 most general way. We have, in the first place, seen that the cat's 

 supreme and governing set of organs, the central part of the nervous 

 system, runs along the back of the animal enclosed in a special tuhe, 

 which is separated from the more ventral part of its body by the 

 vertebral centra. We have also seen that the central part of its 

 circulating system lies above its sternum in the ventral part of its 

 body, with the alimentary canal running between it and the spinal 

 column. The anterior end of that canal we have also seen to end 

 at the mouth, which is placed on the ventral side of the brain. The 

 limbs we have noted as consisting of two pairs, neither more nor 

 less, each supported by a solid internal skeleton. No prolongation, 

 however, of the body cavity or of the alimentary canal enters any of the 

 limbs. We have also seen that its blood is red, and that a portion 

 of the blood, on its way back to the heart, undergoes a secondary, 

 "portal," circulation in the liver. The mouth we have found to be 

 bounded by jaws placed one above, the other below and not laterally, 

 or right and left. In development we have recognised that the first 

 sign of the embryo is a longitudinal groove, beneath which a 

 " chorda dorsalis " is formed, while visceral clefts and arches are 

 temporarily developed on each side of the pharynx the visceral 

 arches taking part in the formation of the jaws. The above charac- 

 ters are characters all of which the cat shares with a certain number 

 of animals not yet here referred to ; namely, with fishes,* frogs, and 

 toads, reptiles, birds and beasts, and lastly, with ourselves also. 

 These creatures together make up another (the ninth and last,) sub- 

 kingdom of animals, the sub-kingdom YERTEBRATA so called because 

 all the creatures which belong to it possess a spinal column, or 

 backbone, made up in most cases (as we have seen it to be in the 

 cat) of a chain of spinal bones or vertebrae. The cat then is one 

 of the group (sub-kingdom) of " backboned animals." All these 

 vertebrate creatures possess a fundamental agreement in organization 

 with the cat, though, as we shall see, they present various and very 

 different degrees of minor structural divergence from it. But the 

 creatures which belong to the other eight sub-kingdoms, though they 

 greatly vary inter se, yet all agree to differ fundamentally from the 

 type of organization presented by the Yertebrata. On this account 

 they are often conveniently spoken of as one whole, under the name 

 Invertcbrata although they cannot be united into one group by any 

 positive characters which are not applicable to all animals whatso- 

 ever. That we may be able the better to appreciate, by contrast, 

 the value of these vertebrate characters which thus exist in the cat, 

 the presence of which is implied when we say that the cat is a 

 backboned animal it may be well to shortly glance at the organiza- 

 tion of one or two of the Invertebrata. 



* There is one fish (the Amphioxus or i ganized than any other vertebrate animals 

 lancelet) which is much more lowly or- I as will be pointed out later on. 



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