PROMORPHOLOGY 



93 



essentially equal. In such a case there may be said to be an infinite number of 

 similar axes, and the poles of each axis are similar. This may be described as 

 universal symmetry. 



Fig. 46. 



Fig 



Pig. 46. Spherical cell (resting stage of Amceba) illustrating general or universal symmetry. 



Any plane passing through the centre will divide it into two essentially equal portions. 



Fig. 47. Amoeba in active condition. Entirely unsymmetrical. 



Question on the figure. — What prevents this animal being a perfect illustration 

 of universal symmetry ? 



Fig. 48. 



Fig. 48. Actinomma aster acanthion, a Radiolarian with a limited number of specialized radii 

 (axes), symmetrically arranged about the centre. A, whole animal with portion of two spheres of 

 shell removed. B, section, showing relation of the protoplasm to the skeleton, n, nucleus; t, 

 protoplasm; sk., skeleton. From Parker and Haswell. 



Questions on the figures. — In what way does this species differ in symmetry 

 from Fig. 46? How many specially developed axes appear to be present? By 

 how many planes may the organism be divided into essentially equal portions? 



2. An organism may be wholly asymmetrical, without any definite form, the 

 axes being without regular arrangement. (Am(Bba in its active stages, Fig. 47; 

 some Sponges.) In other instances the form may be definite and axes developed ; 



