. Elements of Comparative Anatomy. 282 COMPAEATIVE ANATOMY. aa a(r ;f large ventral siuus, placed at tlie base of the gills (in the so-called sternal canal). Each gill (//r) receives a vessel from this sinus (branchial artery). From the gills the blood passes into the branchial veins {vhr), six or seven of which arise on either side of the ]:)ericardial sinus, into -which they often open by funnel- shaped mouths. The valves of the venous ostia are to be regarded as special differentiations of the heart, which aid in dividing it into separate chambers when it is elon- gated. The circulatory
. Elements of Comparative Anatomy. 282 COMPAEATIVE ANATOMY. aa a(r ;f large ventral siuus, placed at tlie base of the gills (in the so-called sternal canal). Each gill (//r) receives a vessel from this sinus (branchial artery). From the gills the blood passes into the branchial veins {vhr), six or seven of which arise on either side of the ]:)ericardial sinus, into -which they often open by funnel- shaped mouths. The valves of the venous ostia are to be regarded as special differentiations of the heart, which aid in dividing it into separate chambers when it is elon- gated. The circulatory system of the Poecilopoda combines several of these different stages ; their elongated heart lies in a pericardial sinus, from which it re- ceives blood by seven pairs of ostia; it does not onlj give off arterial trunks an- teriorly and posteriorly, but from the sides also, as do the Stomapoda. § 218. The circulatory organs of the Tracheata very much resemble the elon- gated multi - camerate hearts found in some Crus- tacea; and the differences are due rather to the de- gree to which the vascular system which passes froin the heart is developed. This again is affected by its relations to the respiratory organs, for when they are. Fig. 145. Diagram of the circulatory sj-stem of a Lobster, o Eye. oe Lateral antennEfi. ai Mesial antennae. br Brancliise. c Heart. J3C Pericardium. oo Median anterior aorta. aa Hepatic artery, a-p Posterior artery of tbe body. aTrunkof the ventral arteiy. ai'Anterior ventral artery, v Ventral venous sinus, v hr Branchial veins. The arrows indicate the direction of the current of blood. limited to a small space the blood-vessels are more perfectly developed, while when the respira- tory organs are distributed over the whole body the arteries are less well developed. The Protracheata appear to resemble them in Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration a
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