. A text-book of invertebrate morphology. Invertebrates. TYPE GBUSTACEA. 377 tremity encroaching but slightly upon the thorax (Isopoda). It is provided with a varying number of openings along its sides, through which the blood gains entrance to its cavity froin. the pericardial sinus—these openings, termed ostia, being guarded by valves opening inwards and preventing regurgitation of the blood during systole. From either end of the heart arteries arise which, after a longer or shorter course and many or few branchings, open widely into the lacunar spaces. From these the blood passes in some fo
. A text-book of invertebrate morphology. Invertebrates. TYPE GBUSTACEA. 377 tremity encroaching but slightly upon the thorax (Isopoda). It is provided with a varying number of openings along its sides, through which the blood gains entrance to its cavity froin. the pericardial sinus—these openings, termed ostia, being guarded by valves opening inwards and preventing regurgitation of the blood during systole. From either end of the heart arteries arise which, after a longer or shorter course and many or few branchings, open widely into the lacunar spaces. From these the blood passes in some forms into a venous sinus situated on the ventral surface of the. Fig. 168.—Diagbam op Stkuctuke op Crustacean (Gambarus). an = anus. ca = carapace. ce = cerebral ganglion. h = heart. i — iutestiue. I = digestive glaud. m = moutL. mp = openiug of vas deferens. ne = nephridium. s = stomach. sa = sternal artery. le = testis. il = telson. vd = vas deferens. vn = ventral nerve. 1-6 = abdominal segments. body, and thence i^ distributed to the branchiae, passing from them back to the pericardial sinus, and so to the heart again. The blood is usually colorless, though occasionally greenish, in which case it contains a respiratory copper-containing pig- ment termed hsemocyauin, or reddish, in which case the pig- ment is haemoglobin. It consists of a plasma in which float amoeboid nucleated corpuscles. The digestive system consists of an almost straight tube extending from mouth (Fig. 168, m) to anus (an) and divisible into three regions. The mouth is bounded in front by an overhanging lip, and behind by a lower lip which arises as two separate parts, which by some writers have been regarded. 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 McMurrich, J. Playfair (James Playfair), 1859-1939. New York, H. Holt and
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