General principles of zoology . greatest regularity in the arrangement oftheir parts, there is not an entire conformity to the de-mands of the fundamental form, so that we are compelled PROMORPHOLOG Y. I5C, to ignore certain greater or less variations. If, for exam-ple, we call man bilaterally symmetrical, we must ignorenot only the slight asymmetry of a nose awry, etc., butalso what is more important—that the liver has beenpushed to the right, the heart to the left, side; and thatthe digestive tract throughout its entire course runs asym-metrically. Symmetry.—Now, according to the three dimen
General principles of zoology . greatest regularity in the arrangement oftheir parts, there is not an entire conformity to the de-mands of the fundamental form, so that we are compelled PROMORPHOLOG Y. I5C, to ignore certain greater or less variations. If, for exam-ple, we call man bilaterally symmetrical, we must ignorenot only the slight asymmetry of a nose awry, etc., butalso what is more important—that the liver has beenpushed to the right, the heart to the left, side; and thatthe digestive tract throughout its entire course runs asym-metrically. Symmetry.—Now, according to the three dimensionsof space, we can pass three axes, perpendicular to eachother, through the body of an animal, and up to a certaindegree may characterize it according to the nature of theseaxes ; further, we may characterize it according to the planesby which it can be symmetrically halved, the plane of sym-metry. Thus we find the following fundamental forms: i. Anaxial, asymmetrical, irregular, or amorphous fun-damental form (Fig. Si).. FIG. 81.—Spongilla Jlutiatilis. (After Huxley.) a, superficial layer with dermal pores ; lieregion of the ciliated chambers; d, osculum. 2. Homaxial, symmetrical in all directions, sphericalfundamental form (Fig. 82). 3. Monaxial, radially symmetrical (Fig. 83). 4. Simple heteraxial, biradially symmetrical (Figs. 84,85). 5. Double heteraxial, bilaterally symmetrical (Fig. 86).i. AnaxialQ*asymmetrical animals, so called, are those JOO GENERAL PRINCIPLES OF ZOOLOGY.
Size: 1627px × 1535px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
