228 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



suckers, or adhesive organs, which serve to grasp its food and to bring 

 it within the mouth. 



In the articulates, in addition to the suctorial contrivance already 

 mentioned, innumerable modifications of the mouth are seen, that being 

 the organ which in this group constitutes the main prehensile organ, its 

 modifications corresponding to the character of the food; thus, the earth- 

 worm has a muscular upper lip, by which it secures the earth which con- 

 tains its food, and which serves to bring it within the mouth. In other 

 worms, again, the gullet is so constructed that it can be turned inside 

 out to form a proboscis for seizing prey. In such instances it is nearly 

 invariably supplied with horny teeth. Millipedes and caterpillars have 

 powerful horny jaws, working horizontally, while the centipedes have a 

 second pair, which are really modified feet, terminating in curved fangs 

 containing a poison-duct. In the crab, the legs and feet serve not only 

 for progression, but also for the mastication of food, as is also the case 

 in the lobster, where the seventh pair of feet are enormously developed 

 and furnished with powerful, crushing pinchers, those on one side of the 

 body being smooth, the other knobbed. Scorpions have, again, a small 

 pair of claws for prehension of food, and a smaller pair of forceps for 

 holding the food in contact with the mouth. In the spider the claws are 

 wanting, and the forceps ends in a fang or hook, which is perforated to 

 convey venom. Biting insects, such as the beetle, have distinct buccal 

 appendages, consisting of two pairs of horny jaws, which open one above, 

 the other below, the oral aperture: the upper are called mandibles or 

 pinchers, the lower the maxilla?, which support the palpi. The former 

 are armed with sharp teeth. The maxillae are similar, but smaller, and in 

 some insects have appendages which are called palpi or feelers, which not 

 only select but hold the food steady while it is crushed by the mandibles 

 and maxilla?. Such appendages represent a free pair of jaws. All 

 invertebrates move their jaws horizontally. 



In all vertebrates the jaws move vertically, and are in many instances 

 the main or sole organ for the prehension of food. In fishes the jaws are 

 always prehensile and often provided with teeth, which, being sharp and 

 curved inward, are prehensile ' organs ; where teeth are absent, as in the 

 sturgeon, the food is drawn in by suction. The hog-fish has a single 

 tooth, which it plunges into its prey and then bores a hole with its saw- 

 like tongue. The fins or tongues of fish are not prehensile. 



In reptiles the jaws, teeth, or tongues may serve as prehensile organs, 

 while in reptiles prehensile lips are never present. Thus, the turtle has 

 a mouth provided with horny jaws, the crocodile sharp, curved teeth, and 

 the frog, toad, and chameleon, glutinous tongues for seizing their food. 

 In chelonians the jaws are horny, and are supplied with small teeth in 

 ophidians ; in the larger saurian s the teeth are powerful, while they are 



