. A manual of zoology. Zoology. ARTHROPODA. 4:03 as was pointed oi^t (p. 12-I-), of a dorsal brain (supraossophageal ganglia) and a ventral chain of ganglia, all connected by longi- tudinal nerve cords, the brain being connected with the rest by cords or commissures passing on either side of the oesophagus. The ventral chain should contain as many joairs of ganglia as there are somites, but this is not the case except in the embryo. The tendency is rather towards a fusion of ganglia, especially of those somites which unite or fuse. This fusion of ganglia occurs to a ABC D. Fig. 405. —Different
. A manual of zoology. Zoology. ARTHROPODA. 4:03 as was pointed oi^t (p. 12-I-), of a dorsal brain (supraossophageal ganglia) and a ventral chain of ganglia, all connected by longi- tudinal nerve cords, the brain being connected with the rest by cords or commissures passing on either side of the oesophagus. The ventral chain should contain as many joairs of ganglia as there are somites, but this is not the case except in the embryo. The tendency is rather towards a fusion of ganglia, especially of those somites which unite or fuse. This fusion of ganglia occurs to a ABC D. Fig. 405. —Different degrees of concentration of tlie ventral cord of Arthropods. (From GeKenbaur.) A, Termite (after Lespfls); B, water beetle (after Blanchard); C\ tly (after Blanchard): Z*, Thelyphonid (after Blanchard). a, abdomen ; g'^, r/^, Kan;;^lia of ventral cord; qi, Infracesophageal ganglion; as, supracesophageal ganglion ; o, eye ; ii'-p'", walking feet; ti\ lung books ; 1, chelicerae ; 2, pedipalpus. varying extent in different species, the extreme being reached in tlie spiders and crabs (fig. 4-1:1), where the whole ventral chain forms a large ganglionic mass. In all cases, however, the brain remains distinct from the rest, its position dorsal to the cesojihagus precluding its fusion with the ventral chain. Of the sense organs the best known are the eyes, of whicli two types are recognized, the simple (ocellus, stemma) and the com- jMiunil (faceted). The ocelli are very small. In their highest development, as in spiders (fig. 400), they are composed of lens, vitreous Ijody, and retina. Tiie lens is formed by the cuticula, the rest from the epidermis. The lens differs from the rest of the cuticle in being transparent, and is usually thickened to a biconcave body (7) which converges the light upon the retina. Behind the lens ccmies a layer of transparent cells, the vitreous body (2), and. Please note that these images are extracted from scanned page images that may have been dig
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
