. Elements of zoology, to accompany the field and laboratory study of animals. Zoology. 244 ZOOLOGY '"Jt'f- amount of nutritive matter. Traces of thin-walled vessels occur; one set accompanies the water-vascular system and a complicated set of capillaries lies in the intestines. No " pulsating " heart is known; hence the fluid must pass only very slowly tlirough these spaces. Organs of ex- cretion are not present, probably because the dis- solved products of decomposition readily pass out through the tube- feet and the skin, which are bathed. Fig. 234. — View of internal organs
. Elements of zoology, to accompany the field and laboratory study of animals. Zoology. 244 ZOOLOGY '"Jt'f- amount of nutritive matter. Traces of thin-walled vessels occur; one set accompanies the water-vascular system and a complicated set of capillaries lies in the intestines. No " pulsating " heart is known; hence the fluid must pass only very slowly tlirough these spaces. Organs of ex- cretion are not present, probably because the dis- solved products of decomposition readily pass out through the tube- feet and the skin, which are bathed. Fig. 234. — View of internal organs of a sea-urchin after removal of the oral half of the body wall. The food canal (aK.) is shown entire, beginning at Ijy constantly re the lantern {lard.) and passing along the a?sophagus ('.) and intestine {ali. ali.) to the rectum (red.). Parts of five ovaries (ov.) are seen arranged around the anus. The blood vessels are represented Ijy a circular vessel around the mouth (or. r. ves.), one around the anus (ah. r. ves.), and a vessel on the in- testine (int. DCS.). The siphon is shown at siph. From Parker and Haswell. newed sea-water. Reproductive Organs. — The sexes are usually separate in echino- derms. The eggs or sperm-cells are usually formed in the walls of pouches opening interradially; in tj^pical sea- urchins, at apertures in five plates lying around the anus. Eggs are poured out and stream down among the spines and often develop there under their protection. Musculature. — Owing to the rigid outer skeleton, a gen- eral body musculature is nearly wanting except in holothu- rians. Muscles move the jaws and the spines of sea-urchins, and these are frequently very 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 Davenport, Charles Benedict, 1866-1944; Davenport, Gertrude Anna Crott
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1911
