. Agricultural zoology. Zoology. 18 ZOOLOGY. between auricle and ventricle, one valve is not enough to make it impossible for the blood to pass back into the auricle during the contraction of the ventricular walls. There are two or three valves there (Fig. 8, KL), fixed by fibres to the wall of the ventricle. In order that the blood which is forced into the artery {) may not pass into the ventricle during its relaxa- tion, there is another valve (not indicated in Fig. 8), at the base of the artery. An arrangement like that so far described is found in fishes. The heart consists in them of
. Agricultural zoology. Zoology. 18 ZOOLOGY. between auricle and ventricle, one valve is not enough to make it impossible for the blood to pass back into the auricle during the contraction of the ventricular walls. There are two or three valves there (Fig. 8, KL), fixed by fibres to the wall of the ventricle. In order that the blood which is forced into the artery {) may not pass into the ventricle during its relaxa- tion, there is another valve (not indicated in Fig. 8), at the base of the artery. An arrangement like that so far described is found in fishes. The heart consists in them of an auricle, into which is returned the blood that has traversed the body, and of a ventricle which moves it on again. But the blood that has traversed the body is on that account poor in oxygen, and consequently unfit to be circulated again when it is returned to the heart. It is necessary for it to take up fresh oxygen before being circulated again. In fishes this difficulty is met by the blood, poor in oxygen, which flows out of the ventricle, first going to the gills and streaming through them. The gills consist of a very large number of small, thin-walled outgrowths arranged in regular rows on the firm gill-arches. The blood, poor in oxygen, passing out of the ventricle and through various arterial branches to the gill-filaments, takes up fresh oxygen as it streams through these from the oxygen dissolved in the water which con- stantly surrounds them. For this purpose a stream of pure water is regularly taken in by the mouth and. Fig, 8.—Diagram of the Heart in a Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bos, Jan Ritzema, 1850-1928; Ainsworth Davis, J. R. (James Richard), 1861-1934. London, Chapman & Hall, Ld.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1894
