572 SPECIAL PHYSIOLOGY. 



animal scale ; and its diversities of form and structure become most obvious 

 in the highest groups. 



The digestive cavity usually takes the form of an alimentary canal, which, 

 in its perfect condition, presents two orifices, an inlet, and an outlet. It is 

 usually divisible into an oesophagus or gullet, a stomach, and an intestine. 

 Its relative length and capacity, and the complication of its superadded parts 

 in any given case, have reference chiefly to the nature of the food. Thus the 

 vegetable-feeding species of any group, be it Order, Class, or Subkingdom, 

 have a longer, more capacious, and more complicated apparatus, than their 

 congeners which live upon animal food. This fact is illustrated by comparing 

 the snail with the oyster, most insects with spiders, the caterpillar with the 

 perfect insect, the tadpole with the perfect frog, the vegetable-feeding turtles 

 and tortoises with the carnivorous fishes, the granivorous with the carnivor- 

 ous birds, and the herbivorous with the carnivorous quadrupeds. 



It is said that the intestine of the domestic cat is longer than that of the 

 wild cat, and even that the same is the case with the vegetarian races of men, 

 as compared with men generally. The greater length and complication of 

 the alimentary canal in vegetable feeders, are owing to their food requiring 

 more prolonged digestion than an animal diet ; its increased capacity is due 

 to the fact, that to obtain a given quantity of nutriment capable of supporting 

 life, a greater bulk of vegetable food is required than of animal food, particu- 

 larly so when that consists, not of fruit and seeds, but of grasses, or the green 

 parts of herbs and trees, as is the case with the food of the Ruminants, Soli- 

 peds, and Pachyderms. 



The digestive apparatus is also modified to suit the physical condition of 

 hardness or softness of the food, and the various modes in which the animal 

 must seize, crop, and masticate it ; hence the existence of modifications in the 

 prehensile and masticatory apparatus, the mouth, teeth, and gizzard. Fur- 

 thermore, the periods of feeding influence the form of the digestive organs ; 

 animals of the same order, Ruminants for example, which feed constantly, 

 having a simpler construction of the stomach than those which, by instinct or 

 necessity, take food or drink at longer intervals ; hence the great capacity of 

 the stomach and large intestine in the Ruminants, Solipeds, and Pachyderms 

 generally, the existence of water-cells in the paunch of the camel, and the 

 presence of large crops in many granivorous birds. In the Class of Birds 

 generally, an example is met with of a modification dependent on the plan of 

 the Class itself; for a heavy external masticating apparatus, connected with 

 the head, being inconsistent with the organic aim of construction for flight, an 

 internal crushing apparatus, or gizzard, is present where the food requires it. 



Prehension of Food in Animals. 



Mammalia. The prehensile limbs of the Quadrumana seize the food, and 

 transfer it to the mouth. In the feline tribe, the paws serve to capture living 

 prey, but do not convey it to the mouth, this being accomplished by move- 

 ments of the head and jaws. In many Rodents, as in the squirrel, rat, mouse, 

 and guinea-pig, and also in the kangaroo, and other Marsupials, the two ante- 

 rior limbs are often used together for holding food, and approximating it to 

 the mouth. In most Mammalia, however, the anterior limbs are organized 

 for locomotion, and the jaws and teeth are the instruments used for capturing 

 or cropping the food, and for its introduction into the mouth. In all cases, 

 the lips are emploved. The act of sucking, characteristic of all young Mam- 

 malia, and that of drinking in the adult, is performed by the lips, cheeks and 

 tongue, and the lapping of the Carnivora, by the latter or^an only. 



Special contrivances for the seizure of the food, are noticed in the snout of 

 the tapir, the proboscis of the elephant, the long tongue of the giraffe, and the 

 extensible viscid tongue of the ant-eaters. The marine and piscine Cetacea, 

 have either rudimentary or no limbs ; some, like the dolphin and porpoise, 

 seize their prey by means of their many-toothed jaws ; the whalebone whale 

 opens its huge mouth, as it moves through the water, which, entering that 

 cavity, filters through the numerous whalebone plates, descending from the 

 upper jaw and fringing the sides of the mouth, and so leaves multitudes of 



