Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 464 CRUSTACEA. as in the youngest larvae of the Decapoda, only one pair of slits is present and the arterial system has but few branches. In the fully- developed Decapoda the number of paired slits is increased by the addition of a dorsal and a ventral pair, and the vascular system is considerably perfected. An anterior cephalic aorta supplies the brain, the antennae and eyes. Two lateral pairs of arteries send branche
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 464 CRUSTACEA. as in the youngest larvae of the Decapoda, only one pair of slits is present and the arterial system has but few branches. In the fully- developed Decapoda the number of paired slits is increased by the addition of a dorsal and a ventral pair, and the vascular system is considerably perfected. An anterior cephalic aorta supplies the brain, the antennae and eyes. Two lateral pairs of arteries send branches to the stomach, liver and generative organs. The posterior abdominal aorta usually divides into a dorsal and a ventral artery, of which the first supplies the muscles of the tail, the latter (known as sternal artery) sends branches to the appendages of the thorax and abdomen (fig. 364). From the ramifications (often capillary-like) the blood flows into larger or smaller canals with connective tissue walls which may be regarded as veins, and from thence into a wide blood space situated at the base of the gills. It thence passes through F' Fro. 364.—Longitudinal section through Aitaca* Jluviatilis (after Huxley). C, Heart; Ac, cephalic aorta; Aa, abdominal aorta, the sternal artery (Sta) is given off close to its origin; Km, masticatory stomach; D, intestine ; Z, liver; T, testis; Yd, vas deferens; Go, genital opening; G, brain; N, ganglionic cord ; Sf, lateral plate of the caudal fin. the gills and, having become arterial, passes into other vascular tracts (branchial veins containing arterial blood), which conduct it to a receptacle surrounding the heart, the pericardia! sinus : from the latter the blood enters the heart through the slits which are provided with valves. The alimentary canal consists of a short oesophagus, a wide saccular crop and an elongated intestine which opens by the anus beneath the median plate (telson) of the caudal fin. The wide crop or masticator
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