NiNTR Annual Meeting. 67 



Taking Rodentia, we find the peculiar feature of the order to be the two strong, 

 curved, cutting, continuously-growing incisors, which are undoubtedly so modified for a 

 purpose. The origin of these specialized teeth must have been the accidental preference of 

 nuts and barks of trees, which induced a variation and developed the peculiar organs, with 

 accompanying modification of the remainder of the denture and of the digestive region. 

 Man}' of tlie members of this order became climbers, to obtain their food more readily, 

 and some species took up tlieir abode in the trunks of trees, living an arboreal life con- 

 venient to their food, and protected by tlie plants that bore it. Some of them became 

 burrowers, in order to obtain roots and barks in the ground and the small grains of low 

 plants, and their burrowing habits soon developed their chief protection against their 

 enemies, many of them becoming so completely adapted in their limbs to this work as to 

 be almost incapable of progression upon level ground. 



In Bradypus, we find a peculiar adjustment of the curious teeth to the mere crushing 

 of the leaves and shoots of trees, and a remarkable conformation of the stomach to this 

 coarse food, it being divided into compartments by transverse ligatures for the longer re- 

 tention of food for digestion. But a most i)ecuiiar feature in these animals is their 

 adaptation to an almost complete arboreal life, by the legs being modified for the suspen- 

 sion of the body beneath the limbs of trees, and its living and moving continually in this 

 position. This peculiarity we claim to be one of the indirect results of food-selection. 



In the giraffe we observe another leaf-eater, whose limbs are modified for a terrestrial 

 existence, while it is enabled to reach the branches of trees by means of elongated neck 

 and legs, these having been developed by a preference for the shoots and buds of trees. 



In the Carnivora we find strong jaws with strong muscles for the exercise of great 

 power in seizing and tearing prey; also a lithe, elastic and powerful systemic framework, 

 for pursuing and overcoming other animals. As their food requires no mastication, there 

 is no lateral movement of the jaws, in the purest forms, but these are merely capal)le of 

 extensive opening and forcible closure. In the vegetable-feeder, on the contrary, the 

 lateral movement capacity of the jaws is largely developed to allow of trituration, while 

 extensive and forcible vertical movement is suppressed. The claws of Felidce may also 

 be reckoned as the product of food-selection, being developed and used in the capturing 

 and tearing of pi'cy. 



A remarkable instance of evidence in our favor is found in some of the Cetacea. Ba- 

 la^nidcr, are noted for tlie absence of teeth, which are superseded by rows of baleen or 

 whalebone, which fringes the opening of the mouth, and by means of which small sea- 

 animals (cliiefly Pteropoda), its food, are strained from the water. This adaptation to 

 this food is comparatively recent, as numerous rudimentary teeth are found in the jaws 

 in early foetal life, evidencing a former condition in which teeth were possessed and used 

 upon different food. The usurpation of these organs by a peculiar growth that is better 

 adapted to the food which plentifully surrounds these animals, indicates a rapid and won- 

 derful power of modification by food -selection. The animal also possesses a very small 

 cesophagns, to guard against the entrance of larger food which has not been reduced for 

 want of teeth. 



We are reminded here of an opposite example of a disproportionate power of deglu- 

 tition — that of ophidia. In these reptiles, the food, often disproportionately large, is 

 swallowed by permission of the articulation of the inferior maxillary and its attachments, 

 which part and separate to a remarkable extent to allow the large object to pass. The 

 denture is formed for seizure and gradual creeping up upon the victim. 



But we cannot go into further minutite. We have thus glanced at some of tlie more 

 specialized forms which furnish most marked evidence ; but the adaptation of form to 

 food is just as perfect in all other species. 



As has been already stated, other conditions being in harmony, the persistence of the 

 food-supply will induce and determine the permanence of a given species or genus. 



