The laws and mechanics of circulation, with the principle involved in animal movement . he blood is being arterialized as it is being ren-dered venous ; hence, no heart is developed, the action in thedorsal artery with the lateral vessels extending into the capil-lary plexuses of the skin, respiratory-vesicles, or branchiae, as NO HEART IN ARENICOLA. 387 the case may be, being sufficient for the purpose and subserv-ing the functions of a heart. But this latter circumstance ismade more conspicuous in arenicola (Fig. 157), in which thecirculation is simplified. And this beautiful diagram, by the
The laws and mechanics of circulation, with the principle involved in animal movement . he blood is being arterialized as it is being ren-dered venous ; hence, no heart is developed, the action in thedorsal artery with the lateral vessels extending into the capil-lary plexuses of the skin, respiratory-vesicles, or branchiae, as NO HEART IN ARENICOLA. 387 the case may be, being sufficient for the purpose and subserv-ing the functions of a heart. But this latter circumstance ismade more conspicuous in arenicola (Fig. 157), in which thecirculation is simplified. And this beautiful diagram, by thedistinguished anatomist and naturalist at Heidelberg, will serveto give a distinct mental picture of the adaptive changes in thevascular system to the form of the respiratory apparatus andthe principle that obtains in the mechanics for increasingcirculation in it commensurate with the force which is ex-pended in the activities. As will be seen, the branchial vessels(b, b) are connected directly with the great dorsal and ventraltrunks (d, v) the blood from the latter passing into the. Fig. 157.—Diagrammatic Transverse Section through the Hinder Half of the Body ofArenicola, to show the arrangement of the vessels.—Gegenbaur. D, dorsal ; V,ventral side ; n, ventral medulla ; i, enteric cavity ; or, branchiae ; v, ventral vascu-lar trunk ; ab, branchial vessels ; d, dorsal vascular trunk ; h, branch surroundingthe enteric canal; v, visceral ventral vessel. branchia ibr) by means of the afferent vessel (a), thence tothe dorsal artery through the efferent vessel (b), one uponeither side corresponding with the branchiae ; hence, any ex-pansile action m the branchiae or vibratory motion tending toincrease circulation in the plexuses would necessarily deter-mine the venous blood in this direction, while the pumping ac-tion in the dorsal vessel should serve for aspirating the plexusesand propelling it through the system ; since the diastoles pro-duce a suction-force and the systoles
Size: 2223px × 1124px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookde, booksubjectblood, booksubjectrespiration
