. Elements of Comparative Anatomy. 284 COjMPAEATR^E axatomy. ~c conuectiou between the external segmentation of the hody, and its internal organisation. Herein we may recognise a lower stage. The chambers (Fig. 147, 2v) are again separated from one another by valves, placed at each venous ostium (o), and are attached by large alas cordis ()»). Paired arterial trunks, which are especially well developed in the Scolopendridge, are sent off from each chamber to its proper metameres. As compared with the Insecta, a higher degree of develop- ment is implied by this arrangement. These arteries arise
. Elements of Comparative Anatomy. 284 COjMPAEATR^E axatomy. ~c conuectiou between the external segmentation of the hody, and its internal organisation. Herein we may recognise a lower stage. The chambers (Fig. 147, 2v) are again separated from one another by valves, placed at each venous ostium (o), and are attached by large alas cordis ()»). Paired arterial trunks, which are especially well developed in the Scolopendridge, are sent off from each chamber to its proper metameres. As compared with the Insecta, a higher degree of develop- ment is implied by this arrangement. These arteries arise at about the level of the venous ostia. In the Julida; they are double, for each chamber is composed of two, which were primitively separate. Three trunks are given off from the most anterior chamber; the median one (c) supplies the cephalic segments, and the two lateral ones (5) surround the oesophagus. Where they unite, a larger trunk is formed, which lies on the ventral nerve-chord; just as in the Scorpionea,this runs as far as the last ganglion of the ventral chain, and gives off numerous branches. § Fig. 117. Head and two segments of the body of Scolopendra, with the most anterior portion of the blood- rascular system. C Head. G Supra- ganglion (Cerebrum). 0 Eyes, il/ Mandibles. A Antennaj. K Chambers of the Heart, m Ala? cordis. 0 Venous ostia. a Lateral arteries. 6 Arterial arches, c Cephalic artery (after Newport). We find that the Scorpiouea among the Arachuida are provided with the most complicated circulatory apparatus. The heart, sur- rounded by a pericardial sinus, is considerably elongated in correla- tion with the form of their body; it is divided into 8 chambers, which are held fast by lateral muscles (alas cordis). A pair of dorsal clefts (venous ostia) leads into each chamber; these clefts may be closed by valves which project into the interior. Arterial vessels are given off from the anterior as well as from the posterior end of the hear
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