. A text-book of agricultural zoology. Zoology, Agricultural; Zoology, Economic. EEPTILIA. 331 less, as one British species, the Adder (Vipei-a berus), is poison- ous, it is as well that we should refer very briefly to them. Lizards, however, are decidedly beneficial, for they feed upon noxious insects, &c. Eeptiles are all provided with a bony skeleton, and may or may not possess legs. The heart is com- posed of four chambers; but the two ventricles are not completely separate, except in the Crocodiles. The heart (fig. 169) functionally only consists of three chambers, although we have an
. A text-book of agricultural zoology. Zoology, Agricultural; Zoology, Economic. EEPTILIA. 331 less, as one British species, the Adder (Vipei-a berus), is poison- ous, it is as well that we should refer very briefly to them. Lizards, however, are decidedly beneficial, for they feed upon noxious insects, &c. Eeptiles are all provided with a bony skeleton, and may or may not possess legs. The heart is com- posed of four chambers; but the two ventricles are not completely separate, except in the Crocodiles. The heart (fig. 169) functionally only consists of three chambers, although we have an advance towards the typical completely four-chambered organ. The circulation in Eeptiles is as follows: the impure blood is returned from the body by the large veins (r) and emptied into the right auricle (a); from the auricle it passes on to the ventricle (i'). The pure arte- rial blood from the lungs enters into the left auricle (a!) and then into the ventricle. Thus the ventricle with its incomplete septum contains mixed blood much as in the frog, this mixed blood being sent by the ventricle to the lungs by the pulmonary artery (p) and to the body by the aorta (o). We thus get a stage higher than in the Amphibia. Reptiles, then, like Amphibia, are cold- blooded animals of sluggish habits. They reproduce like Birds, oviparously, the eggs being often laid in strings ; the shells may be hard, but are sometimes soft. All the Crocodilia and most Tortoises lay eggs with a shell just as thick and hard as that of birds. Eeptile eggs are incubated by the heat of the sun or by the warmth generated by decaying vegetation in which they are often laid. A few cases of an ovoviviparous nature occur,—for. Fig. 169.—Diagram of the Circulation in Reptiles. a, Right auricle ; a', left auvicle ; v, arterio-venous yen- tricle ; p, pulmonary artery; 0, aorta, (Nicliolson.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabil
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1899
