FORMS OF LIFE 



the basal pole or ground surface; as we find in the oval form, 

 the planoconvex lens, the hemisphere, the cone, etc. Both 

 sub-classes of the monaxonia, the allopola (conoidal) and the 

 isopola (spheroidal), are found realized frequently in organic 

 forms, both in the tissue -cells of the histona and the inde- 

 pendently living protists (A-f, 4, 84). 



In the stauraxonia the vertical imaginary principal axis is 

 cut by two or more horizontal cross-axes or radial-axes. This 

 Is the case in the forms which were formerly generally classed as 

 regular or radial. Here also, as with the monaxonia, we may 

 distinguish two sub-classes, isopola and allopola, according as 

 the poles of the principal axis are equal or unequal. 



Of the stauraxonia isopola we have, for instance, the double 

 pyramids, one of the simplest forms of the octahedron. This 

 form is exhibited very typically by most of the acantharia, the 

 radiolaria in which twenty radial needles (consisting of silicated 

 chalk) shoot out from the centre of the vertical chief axis. 

 These twenty rays are (if we imagine the figure of the earth with 

 its vertical axis) distributed in fiye horizontal zones, with four 

 needles each, in this wise: two pairs cross at right angles in the 

 equatorial zone, but on each side (in north and south hemi- 

 spheres) the points of four needles fall in the tropical zone, and 

 the points of four polar needles in the polar circles; twelve 

 needles (the four equatorial and eight polar) lie in two meridian 

 planes that are vertical to each other; and the eight tropical 

 needles lie in two other meridian planes which cross the former 

 at an angle of forty-five degrees. In most of the acantharia (the 

 radial acanthometra and the mailed acanthophracta) — there 

 are few exceptions — ^this remarkable structural law of twenty 

 radial needles is faithfully maintained by heredity. Its origin 

 is explained by adaptation to a regular attitude which the 

 sea-dwelling unicellular body assumes in a certain stage of 

 equilibrium (A-f, 21, 41). If the points of the real needles are 

 connected by imaginary lines, we get a polyhedrical body, which 

 may be reduced to the form of a regular double pyramid. 

 This typical form of the equipolar stauraxonia is also found in 

 other protists with a plastic skeleton, as in many diatomes and 

 desmidiacea (A-f, 24) . It is more rarely found embodied in the 

 tissue-cells of the histona. 



Unequipolar stauraxonia are the pyramids, a fundamental 

 form that plays an important part in the configuration of 

 organic bodies. They were formerly described as regular or 

 fundamental forms. Such are the regular bloonis of flowering 

 plants, the regular echinoderms, medusae, corals, etc. We may 



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