A treatise on zoology . scales other than den-ticles, and the formation of the jaws from the palato-quadrate barand Meckels cartilage, distinguish them from the rest of the Pisces. The classification of the Chondrichthyes still presents many diffi-culties. The first two sub-classes described lielow (Elasmobranchiiand Pleuracanthodii) have many characters in common, and aredistinguished from all other Pisces by the development in the maleof copulatory claspers. These are specialised posterior portionsof the pelvic fins. It seems very unlikely that the claspers shouldhave been developed independ
A treatise on zoology . scales other than den-ticles, and the formation of the jaws from the palato-quadrate barand Meckels cartilage, distinguish them from the rest of the Pisces. The classification of the Chondrichthyes still presents many diffi-culties. The first two sub-classes described lielow (Elasmobranchiiand Pleuracanthodii) have many characters in common, and aredistinguished from all other Pisces by the development in the maleof copulatory claspers. These are specialised posterior portionsof the pelvic fins. It seems very unlikely that the claspers shouldhave been developed independently in the Elasmobranchs and inthe Pleuracanthodians.^ At the same time, to unite these twogroups into one sub-class would perhaps be to separate them too farfrom the Cladoselachii. Until the structure and affinities of thelatter are better understood, it cannot be decided whether they are ^ For a discussion of the morphology of the skeleton of the paired fins, seepp. 73, 106 ; for the coimlatory claspers, see p. Fig. S3. Diagriun of a section through the dorsaltin of Seyllivvi. ct, ceratotrich ; d, denticle;;?, endoskeletal radial. (From Quart. sn.) 124 CHONDRICHTH \ ES Elasmol3ranchs which have lost the daspers, or an early offshoot RECENT PLIOCENE MIOCENE EOCENE CRETACEOyS JURASSII TRIASSIC CARBONIF-EROUS
Size: 1138px × 2194px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
