. A manual of zoology. Zoology. PROMORPHOLOGY rV. Promorphology; the Fundamental Forms. 123 The structure of the individual animal depends uf on the definite arrange- ments of its organs, which are definite or only vary slightly in each group. Comparison shows that there are a few fundamental forms which play the same role in morpliology as the crystal forms in mineralogy. But there is an important difference. A crystal is made up of similar parts, its form is the result of its physico-chemical composition. This condition cannot exist in animals as each organ is a complex of many chemical comp
. A manual of zoology. Zoology. PROMORPHOLOGY rV. Promorphology; the Fundamental Forms. 123 The structure of the individual animal depends uf on the definite arrange- ments of its organs, which are definite or only vary slightly in each group. Comparison shows that there are a few fundamental forms which play the same role in morpliology as the crystal forms in mineralogy. But there is an important difference. A crystal is made up of similar parts, its form is the result of its physico-chemical composition. This condition cannot exist in animals as each organ is a complex of many chemical compounds. Nor, even where the symmetry is the most pronounced is there that matlrematical accuracy found in crystals. The form of an animal depends upon its extension in space, and accordingly we may pass through it three axes at right angles to each other, these defining the position of three planes. According to the relations of the body to these we may define five fundamental FlG. 88.—Sponge, Lophocalyx philippensis, with buds (after F. E. Schuize). Asymmetrical (anaxial) animals (fig. 88) are such as have no definite arrange- ment of parts with regard to axes or planes, the body growing irregularly in any direction as in many sponges and protozoa. Spherical (homaxial) animals have the parts arranged around a central point, through which innumerable axes and planes may be passed, each plane dividing the whole symmetrically as in some spherical protozoa, chiefly radiolaria (fig- 89)- . . , . , . In radial (monaxial) symmetry there is a main or longitudinal axis which lies in the direction of growth. It may be longer, shorter or of the same length of the other axes, but it may be distinguished by the fact that it passes through parts, as the mouth, which are not found in other axes. Around this main axis the parts of the body are symmetrically arranged, like the spokes of a wheel, so that any plane passing through the main axis will divide the body into symmetrical part
Size: 1640px × 1524px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
