A treatise on zoology . nd ofthe nerve-plexus both before and behind the fins [46], the con-centration of the fins, the frequent presence of a greater numberof buds in earlier than in later stages, the presence in some fish(such as Pristiurm and ScyUiiim: Dohrn [118], Braus [47, 50])of such buds in all the trunk segments, may be considered asevidence supporting Balfours view of the original continuity of thefolds. It has been convincingly shown (Thacher [434], Mivart [300])that the various types of the endoskeleton of the median fins offishes, with more or less well-develof)ed basal plates, or
A treatise on zoology . nd ofthe nerve-plexus both before and behind the fins [46], the con-centration of the fins, the frequent presence of a greater numberof buds in earlier than in later stages, the presence in some fish(such as Pristiurm and ScyUiiim: Dohrn [118], Braus [47, 50])of such buds in all the trunk segments, may be considered asevidence supporting Balfours view of the original continuity of thefolds. It has been convincingly shown (Thacher [434], Mivart [300])that the various types of the endoskeleton of the median fins offishes, with more or less well-develof)ed basal plates, or rays branchingfrom an axis (Figs. 48-50, 52), have been formed from a series ofprimitively discrete segmental radials (soniactidia) by a concrescenceor fusion of their bases, often accompanied by concentration orgathering together at the narrow base of the fin (p. 106). That thesimilar manifold types of the endoskeleton of the paired fins have 76 PAIRED FINS arisen in the same way can scarcely be doubted. Indeed, it is. Dorsal fins, with tlie eiuioskeleton exposed, of: A, NotUlaiins (Heptaitchtts) ciiiereus, Gin. ;B, (ringlymostoma clrmtum, Gm. ; C,Zygaena nwlleas, Risso ; D, Ehynchobatus djedde>;!is, Forslc.(After Mivart.) ;, anterior radials lying on vertebral column ; , anterior radial ; b,longitudinal basal; , basal ; , distal segment of radial; /, fin web supported by ceratotrichia ;;, median segment of radial; ; posterior radial; , proximal segment of radial. Thesefigures illustrate the formation of basals by the concrescence of radials.
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
