Elements of biology, with special Elements of biology, with special reference to their rôle in the lives of animals elementsofbiolog00buch Year: 1933 LATERAL ANTERIOR >. II POSTERIOR MEDIAL Fig. 8o.—Diagrams to show the planes of symmetry and orientation in radial and bilateral forms. spherically symmetrical if its parts are identically placed with refer- ence to a point. Among the Protozoa a colony of volvox is spheri- cally symmetrical, as are also typical metazoon blastul^e (Fig. 77), but no spherically symmetrical adult Metazoa occur. In the diplo- blastic animals, Porifera and Ccel

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Elements of biology, with special Elements of biology, with special reference to their rôle in the lives of animals elementsofbiolog00buch Year: 1933 LATERAL ANTERIOR >. II POSTERIOR MEDIAL Fig. 8o.—Diagrams to show the planes of symmetry and orientation in radial and bilateral forms. spherically symmetrical if its parts are identically placed with refer- ence to a point. Among the Protozoa a colony of volvox is spheri- cally symmetrical, as are also typical metazoon blastul^e (Fig. 77), but no spherically symmetrical adult Metazoa occur. In the diplo- blastic animals, Porifera and Ccelenterata, the symmetry is radial, that is, the parts are symmetrically arranged in imaginary planes which pass through a common axis (Fig. 80). Such organisms appear to be ineffectively oriented for locomotion and this type of symmetry is not extensively characteristic of animals. Plants, how-

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