. Animal and vegetable physiology considered with reference to natural theology. Natural theology; Physiology; Plant physiology; Biology. 2:]0 THE VITAL FUNCTIONS. 346* blood are thus continually intermixed in the course of the circulation.* This is well exemplified in the PlanaricB^ which are a tribe of flat vermiform ani- mals, in many respects allied to the more developed Entozoa, and appearing placed as an intermediate link between them and the Annelida. In many species, such as the Planaria nigra, fusca, and tre- mellaris, (Muller), Duges observed two longitudinal trunks (Fig. 346*) runni
. Animal and vegetable physiology considered with reference to natural theology. Natural theology; Physiology; Plant physiology; Biology. 2:]0 THE VITAL FUNCTIONS. 346* blood are thus continually intermixed in the course of the circulation.* This is well exemplified in the PlanaricB^ which are a tribe of flat vermiform ani- mals, in many respects allied to the more developed Entozoa, and appearing placed as an intermediate link between them and the Annelida. In many species, such as the Planaria nigra, fusca, and tre- mellaris, (Muller), Duges observed two longitudinal trunks (Fig. 346*) running along the sides of the under surface of the animal, and joining together, both at their fore and hind extremities, so as to form a con- tinuous channel of an oval form. A great number of smaller vessels branch oft' from these main trunks in every direction, and ramify exten- sively ; often uniting with those from the opposite side, and establishing the freest communications between them. In the Annelida which have a more lengthened and cylindric form, the principal vessels have a longitudinal course; but are differently disposed in different species. There is in all a vascular trunk, extending along a middle line, the whole length of the back, and especially designated as the dorsal vessel: sometimes there are tw^o such vessels, one on each side of the median line ; and frequently these two vessels unite to form a single trunk as they proceed towards the head. In ge- neral there is also a corresponding trunk, occu-. * For the clearest account of the circulation in the Annelida, see a memoir by Milne Edwards, in the Annales des So. Nat. serie 2, x, 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 Roget, Peter Mark, 1779-1869. London : W. Pickering
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