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. 



§ 220. 



Fig. 1 17. Head and two segments of 

 the body of Scolopendra, with the 

 most anterior portion of the blood- 

 rascular system. C Head. G Supra- 

 oe.sophageal ganglion (Cerebrum). 

 Eyes, il/ Mandibles. A Antennaj. 

 K Chambers of the Heart, m Ala? 

 cordis. 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 heart, 

 of which they are direct prolongations ; the anterior one, the aorta, 

 enters the cephalothorax, while the hinder one runs to the tail. In 

 addition to these a number of lateral arteries are given off close to 

 the venous ostia, and are distributed to the neighbouring organs. 

 Two of the numerous branches given off by the aorta form a vascular 

 ring around the oesophagus, whence an artery runs back (arteria 

 supraspinalis) on, and as far as the end of, the ventral nerve-chord; this 

 artery gives off a large number of branches. The venous blood is 

 collected into a receptacle which lies directly on the ventral surface, 

 just as in the higher Crustacea; from this it is carried to the 



