. A text-book of comparative physiology [microform] : for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative; Veterinary physiology; Physiologie comparée; Physiologie vétérinaire. 119 COMPARATIVK PnY8I0U)0T. Venn cavas •uperiorai; but in many nwDimabi, among which ia man, the left vena cava Bupttrior diaappeani during foetal life. For the preaent wo may tiimply My that the hiatoriea uf the derelopment of the heart, thu blood-veMeb, and the bluud itaelf are cloaely related to each other, and to the nature and ohangea of the various metboda in wliich oxygen
. A text-book of comparative physiology [microform] : for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative; Veterinary physiology; Physiologie comparée; Physiologie vétérinaire. 119 COMPARATIVK PnY8I0U)0T. Venn cavas •uperiorai; but in many nwDimabi, among which ia man, the left vena cava Bupttrior diaappeani during foetal life. For the preaent wo may tiimply My that the hiatoriea uf the derelopment of the heart, thu blood-veMeb, and the bluud itaelf are cloaely related to each other, and to the nature and ohangea of the various metboda in wliich oxygen ia aupplied to the blood and tiaauea, or, in other wordH. to the development of the respir- atory ayatem. I THB OIVBIiOnUMT OF TBI USOOBMlTAZi STBTSBI. Without knowing the hiatory of the organa, the anatomical relatione of parta with uaes ao unlike aa reproduction on the one hand and excretion on the other, can not be comprehended; nor, aa will be abortly made clear, the fact that the aame part may aerve at one time to remove waste matters (urine) and at an- other the generative elementa. The vertebrate excretory ayatem may be divided into three parta, which result from the differentiation of the primitive kid- ney which hum been effected during the alow and gradual eve- lution of vertebrate forma: 1. The head-kidney (pnmephrM). i. The Wolffian body (memmephroa). 8. The kidney proper, or inetatufpAroa. But in thia inatance, as in others to some of whidi alluaion has already been made, these three parta are not funotiooal at the same time. Hie pronephros arises from the anterior part of the segmental duct, pronephrio duot, duct of primitive kid- ney, and archinephric duot, and in the fowl is apparent on the third day; but the pronephros ia beet developed in the ichthy-. Fio. lis.—DUmmi lllnttnitiiig developmeiit of nmnaphro* In th* fowl (Haddim). ao, aorU; b. e, body-cavity; tp, •plbuwt with It* epitrlcblal (fl«ttcn«d) layer; Ay, hypoblaat: m.«, meaoblaatie aonute; i
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