Page:The New International Encyclopædia 1st ed. v. 17.djvu/60

KEPTILE. 44 jaws are adapted, by their mobility and subdi- vision into segments, to open very widely, and the esophagus is eapable of great dilatation. The tongue is conimonlj' free, elongated, and bifid, except in the crocodiles, in whieh it is immovable, whence the popular idea that these animals do not possess this organ. The stomach is sometimes scarcely larger than the a-sophagus and intes- tines {as in .seri)ents), while in other cases it forms a sac of consiilcnilih' size. In eillier case it is capable of great dilatation. A liver, pan- creas, anil sph'cn are always present, the two former pouring their secretions into the upper part of the intestine, which is short, wide, and not much twisted, and divided into two por- tions, corresponding to the small and large intes- tines of mammals, l)y a valve. It finally termi- nates in a wide cloaca, into which the ducts of the urinary and generative organs usually open. The kidneys dill'er from those of ampliiliians, and agree with those of birds, in having no nephro- stomes, and in having each its one separate ureter. See Alimentary Sy.steii, Evolution of. Reptiles breathe air only by means of lungs, and never have gills even during embryonic life. The lungs are usually of large size: but as they are not subdivided, as in manunals and birds, into innumerable microscopic air-cells, the real aerat- ing surface is comparatively small. In several groups they are merely capacious bags, whose vascular or aerating surface is but slightly in- creased by sacculi devcloijcd in their cells. In ser- pents one lung (usually the right one) is of ex- traordinary length, while the other remains alto- gether ruclimentary. This inferiority of the re- spiratory apparatus of reptiles is further shown in the absence of those means for the continuous introduction and exp,:lsion of air possessed by birds, and still more by mammals. See Re- si'iRATOKY System, Comparative Anatomy of. This feeble respiratory system is correlated with the absence of any covering, such as hair or feathers, which might retain the bodily heat gen- crated by the oxygenation of the blood, as is the case in the well-clothed birds and mammals: hence the blood remains at a temperature little above that of the air or water in which the.se ani- mals live, and reptiles are placed with the sim- ilarly naked or scaly amphibians and fishes as 'poikilothermous' or 'cold-blooded.' (See Ani- mal Heat.) The heart, unlike that of a bird or mammal, is divided into two atria, and an im- perfectly divided ventricle: it has no conus, but semilunar valves exist at the base of the tripar- tite aortic trunk: the right and left aortic arches are complete and remain functional. The red corpus(des of the blood are nucleated, biconvex and oval — a point of distinction from mammals. The brain and nervous system present no pecu- liarities calling for special remark; the presence of an intcrcranial hypoglossal nerve separates this class from the amphibia. The organs of the senses are well developed, but there are no lateral sense organs. Xo reptiles have external ears, but their hearing is good. See Nervous System, Evolution of. The sexes are always separate; and the male generative organs, which are far more highly developed than in ainphibi-ans, present peculiari- ties which, in association with the position of the anal aperture, have tieen adopted by zniilogists as a basis of classification of special taxonomic value REPTILE. among the Ophidia. Fertilization is alwaj's in- ternal, and most reptiles lay nidroblastic eggs, from which the young hatch quickly under the influence of the warmth derived from the hot sand or decaying vegetation in which they are buried by the mother, or, in a very few cases, by her incuba- tion. The eggs are comparatively few (except in the turtle tribe), and relatively large, containing a large quantity of food-yolk, so that the oung are able to take CJtre of themselves the moment they emerge ; yet in most cases they receive some parental care. The integument of the eggs is parchuient-like, containing little lime, and the color is always white. Certain reptiles, however, retain their ova in a sort of uterine cavity, formed by a dilatation of the oviduct near its termination in the cloaca, luitil the development of the em- bryo is so far advanced that the enveloping mem- brane bursts previously to the expulsion of the ovum, so that the young are actually born alive — • a mode of generation to which the term 'ovovivip- arous' is applied. An amnion and an allantois are formed in the process of development, allying reptiles with birds and mammals. See Eepbo- DUCTiVE System, Compar^vtive Anatomy of. In past times reptiles have dominated the eartli, swarming in the seas, along the shores, on the land, and in the air. They reached huge size, and many were herbivorous, and preyed upon by others which, as they increased in size and power, must have been the principal active agency in the extermination of the fishes, amphibians and great cuttlefishes, which previous to the Mesozoie Age were the dominant animals of the earth. The al- terations of ph3-sical conditions, which seem to have progressed steadily during the ilesozoic Age, toward dryness and coolness in the atmos- phere, as well as toward elevation and drain- age of the land, and the gradual increase of density (salinity) in the sea, were probably unfavorable to the reptilian forms of that time, botli directly and indirectly, by being likewise un- favorable to the creatures upon which they fed. On the other hand, the growing clarification of the atmosphere consequent ujion the draining and ele- vation of the land and the spread of terrestrial vegetation, which subtracted its excess of carbonic acid gas and contributed a largier amount of oxygen, stinuilatcd the development of superior types which began in the Permian and slowly won their w'ay in competition with the dinosau- rian and other reptiles of their day until they finally overcame them in importance. That they were enabled to do so was due principally, no doubt, to their warmer covering (feathers and hair), enabling them to retain bodily heat, which gave them greater endurance of famine and cli- matic adversities, and promoted activity, which, in turn, reacted to .stimulate and develop all the bodily parts and functions. At any rate the rep- tiles have steadily declined, many of their branches have become extinct, and others are ap- proaching that end, while all have been driven by competition to the holes and corners of the world, to hiding in .swamps, or amid loose rocks, or in hollow trees or among their leafy tops — places where their many enemies cannot easily get at them. Only the heavily armored turtles and croc- odiles are able to survive freely in the water, land-tortoises existing only by being very small, well protected, and secretive: and lizards only by liaving diminished to small size and acquired