. Elementary text-book of zoology. Zoology. 110 VEETEBRATA. by Aristotle, who called them " animals with blood" (vol. I., p. 132); he also put forward the possession of a bony or cartilaginous skeletal axis as a common characteristic. But it was Lamark who first recognised the presence of a vertebral column as the most important character, and introduced before Cuvier the name of Vertebrata into the science. This designation, however, in its strict significance, is only an expression for a definite grade of develop- ment of the skeleton, which may persist in its first unsegmented con
. Elementary text-book of zoology. Zoology. 110 VEETEBRATA. by Aristotle, who called them " animals with blood" (vol. I., p. 132); he also put forward the possession of a bony or cartilaginous skeletal axis as a common characteristic. But it was Lamark who first recognised the presence of a vertebral column as the most important character, and introduced before Cuvier the name of Vertebrata into the science. This designation, however, in its strict significance, is only an expression for a definite grade of develop- ment of the skeleton, which may persist in its first unsegmented condition as the notochorcl (Amphioxus, Myxine). The most im- portant characteristics therefore of the Vertebrata do not depend upon the presence of internal vertebrae and of a vertebral column, but upon a combination of characters which have to do with the general relations of posi- "-•-// \ \ tion, the mutual arrangement of the organs and the mode of embryonic development. We may accordingly define the Vertebrata as laterally symmetrical organisms with an axial skeleton, on the dorsal side of which is placed the central nervous system (brain and spinal cord), while on it's ventral side lie the alimentary canal with its two open- ings (oral and anal) and the rest of the viscera and the heart; the latter being placed on the ventral side of the alimentary canal. 569,-Transverse section The presence of an in- through the chorda dorsalis ternal skeleton is a character of great im- (CA)of the larva of Jinm/ii, mtor ITTI -i • ,1 T ignem (afterGotte). c/,s,Noto- Portance- whlle m the Invertebrates the chordai sheath; sk, skeietoge- firm supporting structures are almost always nous layer; N, spinal cord. j , produced by the hardening and segmenta- tion of the external skin, in the Vertebrates the relation of the hard to the soft parts of the body is reversed. The hard parts are ' placed in the axis of the body, and send out processes towards the dorsal and ventral
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
