. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. 1 hi! ni !iS^!- M. 178 OF AMPIllOXUS. instinct to assume that position, but rather because they cannot help it. It is apparently in consequence of a misunderstanding of ihis observation that Korschelt and Hkider ascribe the larval asymmetry of Amphioxus to the same causes which brought about the asymmetry of the Pleuronectidae. Another, and, as it appears, a still more impossible view, has recently been expressed by van WijHE. According t
. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. 1 hi! ni !iS^!- M. 178 OF AMPIllOXUS. instinct to assume that position, but rather because they cannot help it. It is apparently in consequence of a misunderstanding of ihis observation that Korschelt and Hkider ascribe the larval asymmetry of Amphioxus to the same causes which brought about the asymmetry of the Pleuronectidae. Another, and, as it appears, a still more impossible view, has recently been expressed by van WijHE. According to van Wijhe, the left-sided mouth occupies its normal and primitive position in the larva of Amphioxus, and in that position it represents a gill-slit, whose antimore is the club- shaped gland. Van Wijhe arrived at this view as a result of his very important discoveries as to the musculature and innervation of the adult mouth. These discoveries may be summarised as follows: — 1. The outer muscle of the oral hood represents the anterior continuation of the left half only of the transverse and subatrial muscles. 2. The inner nerve-plexus of the oral hood is on both sides, exclusively from nerves which arise from the leit side of the central nervous system. 3. The velum is innervated entirely from nerves of the left side. From these observations van Wijhe concludes that the mouth of Amphioxus, even in the adult, is essentially an organ of the left side, and is neither homologous with the Ascidian nor with the craniate mouth. It would seem, however, that the more obvious and justifiable interpretation of these facts is that the asymmetrical musculature and innervation described by van Wijhe are merely the partial persistence in the adult of the more complete asymmetry of the larva. Van Wijhe's observations, therefore, do not affect the of the cause of the asymmetry in any degree. 14. (p. 165.) As first shown by Dohrn, the hypophysis of Ammocoetes first aris
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectfishes, bookyear1894
