. A manual of zoology. PHYLUM ARTHROPODA 249 The blood-vascular system is, in comparison with the other systems of organs, not very highly developed, the need of an elaborate system of vessels being greatly diminished by the thorough way in which all the organs are supplied with oxygen by means of the trachea?. The blood is colour- less, or faintly yellowish or green- ish. A contractile tubular heart divided internally into a row of eight chambers by a system of valves extends through the abdo- men on the dorsal aspect. The nervous system (Fig. 148) is on the same general plan as in the Crusta
. A manual of zoology. PHYLUM ARTHROPODA 249 The blood-vascular system is, in comparison with the other systems of organs, not very highly developed, the need of an elaborate system of vessels being greatly diminished by the thorough way in which all the organs are supplied with oxygen by means of the trachea?. The blood is colour- less, or faintly yellowish or green- ish. A contractile tubular heart divided internally into a row of eight chambers by a system of valves extends through the abdo- men on the dorsal aspect. The nervous system (Fig. 148) is on the same general plan as in the Crustacea. There is a double supra - oesophageal ganglion or brain (or), a sub-cesophageal ganglion (in/), also double, and a series of thoracic and abdomi- nal pairs of ganglia, which are closely united together in the middle line. The brain is rela- tively large in the higher insects, and is divided into several It gives off nerves to the antenna? and ocelli and the labrum, and on each side it gives off a large lobe, the optic ganglion, on which the compound eye rests. A pair of oesophageal connectives (conn) pass backwards on either side of the mouth from the brain to the sub-oesophageal ganglia. These connectives are very short, and, as a consequence, the brain and sub-cesophageal. Fig. 148. — Periplaneta. view of the nervous abd. 6, sixth abdominal g ant, antennary nerve ; by, brain ; conn, oesophageal connective ; iiif, sub-cesophageal ganglion ; opt, optic nerve : thoy. /, thoy. 2, thor. 3, first, second, and third thoracic ganglia. (After Miall and Denny.). 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Haswell, William A. (William Aitcheson), 1854-1925. New York, The Macmillan Company; London, Macmillan & Co. ,Ltd.
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