. The elasmobranch fishes. Chondrichthyes. TPIE ELASMOBKANCH FISHES 247 the nervous collector (fig. 224) as in Heptanchus. This has been studied in a number of forms by Braus (1898). Extremes of variation obtain in the num- ber of nerves taking part in this collector. In primitive forms, as in Hep- tanchus, the number may vary greatly and the collector may consist of multi- tudes of strands wliich may or may not fuse together. A good example is Chlamydoselachus (fig. 224), in which the twenty-fifth to the thirty-eighth nerves take part. In other forms few nerves take part in its formation (Spi
. The elasmobranch fishes. Chondrichthyes. TPIE ELASMOBKANCH FISHES 247 the nervous collector (fig. 224) as in Heptanchus. This has been studied in a number of forms by Braus (1898). Extremes of variation obtain in the num- ber of nerves taking part in this collector. In primitive forms, as in Hep- tanchus, the number may vary greatly and the collector may consist of multi- tudes of strands wliich may or may not fuse together. A good example is Chlamydoselachus (fig. 224), in which the twenty-fifth to the thirty-eighth nerves take part. In other forms few nerves take part in its formation (Spinax) or no collector as such is found (Squatixa, Eaja, fig. 223).. Fig. 225. Sympathetie nervous system, Scyllium canicula. (From Botazzi.) , dorsal aorta; , sympathetic fibers to stomach (st.) ; , sympathetic ganglia. The collector has been studied in great detail as to the relation wliich it bears to the origin of paired fins. By those who hold to the gill-arch theory of origin of the fins the collector is an argument for the posterior migration of the pelvic fins, while those who accept the lateral fin-fold theory believe that the collector shows principally that the paired fins formerly had a wider ex- tent than they have at the present time. A greater extent is indicated further by the fact that there may be a plexus posterior to the pelvic fin (fig. 224). In Chlamydoselachus the posterior collector (fig. 224) comprises a num- ber of segments. In the embryo of Acanthias a posterior collector is present, although it is absent in the adult. The pelvic plexus in Eaja vomer is shown in figure 223. SYMPATHETIC OR AUTONOMIC NERVOUS SYSTEM Although the sympathetic nervous system has been studied by many workers but little is known concerning its form in the different Elasmobranchs. It ex- tends from the region of the head to the posterior part of the kidney or meso- nephros. The ciliary ganglion in the region of the oculomotor nerve represents the sympathetic system i
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