. The physiology of the Invertebrata. the shell, the blood can be dis-tinctly seen passing along the upper edge of each branch tothe extremity, then turninground, and flowing back alongthe lower edge to the scape(Sars). In the higher Crustacea, theheart and circulatory appa-ratus are far better definedthan in the lower orders ofthis class. The heart of JIo-7nanis is .a powerful quadrateorgan, and the arteries arelarge, definite in number andin distribution. There arecontractile expansions ( gill-hearts) at the base of theblood-yessels conducting the blood to the branchiae. The heart consists o
. The physiology of the Invertebrata. the shell, the blood can be dis-tinctly seen passing along the upper edge of each branch tothe extremity, then turninground, and flowing back alongthe lower edge to the scape(Sars). In the higher Crustacea, theheart and circulatory appa-ratus are far better definedthan in the lower orders ofthis class. The heart of JIo-7nanis is .a powerful quadrateorgan, and the arteries arelarge, definite in number andin distribution. There arecontractile expansions ( gill-hearts) at the base of theblood-yessels conducting the blood to the branchiae. The heart consists of a single con-tractile cavity, and the arteries in the higher Crustacea areclosed tubes; but the venous blood passes back through theinterstices between the organs of the body, until it reachescertain cavities or reservoirs situated at the bases of the limbs(Fig. 43); therefore the venous blood bathes all the the reservoirs or sinuses the blood passes to the bran-chiae, where it becomes aerated by contact with the Fig. 43. — Vertical Section of aCrustacean, showing the CourseOF THE Blood. a = gill, i = vessels which collect theaerated blood from gills, c =: vesselsconducting venous blood to gills,rf = heart, e = carapace. /=bran-chiocardiac vessels. g = = venous sinus. 200 PHYSIOLOGY OF THE INVERTEBRATA. and then passes through proper vessels to the heart. Itwill be seen that the circulation in the higher forms is semi-vascular and semi-lacunar. The circulatory apparatus of Astacus is well defined. Theheart is situated dorsally and behind the stomach. It issurrounded by the so-called pericardium, which is in reality ablood-sinus; consequently the heart is suspended in a blood-sinus. There are six apertures in this organ provided withvalves which open inwards. These allow the blood to enterthe heart during the diastole, and prevent its egress, exceptby the arteries, during the systole. There are six arterialtrunks provided with valves at their co
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectinverte, bookyear1892
