102 Ke JANDERSON [AUGUST 
seem odd that the two forms of prisms that the trimerous and penta- 
merous symmetries suggest are asymmetric. The fact that arboraceous 
monocotyledons dwell in the tropics, and that dicotyledons dwell in 
temperate regions, has been commented on. The Dicksonias of New 
Zealand and the araucarias of South America have chosen curious 
places for homes. The sun in rotating on its axis, in sending its 
rays through an atmosphere that partly polarizes the rays which are 
going through the air with various degrees of obliquity, and the same 
luminary in having its countenance affected by spots occasionally, not 
to speak of the various wave whirls that may affect rays going in 
different directions, may be held responsible for some of these dis- 
crepancies. The rays, if they are of such a nature as to be alterable 
by a crystal, may be naturally expected to have some power to alter 
the character of a crystal, or other substance, and so a crystal may get 
a molecular twist, and the plant that uses the crystal as food may 
become similarly influenced, or get directly altered itself; but although 
there may have been a tendency to molecular twisting in the young 
plant by the sun’s rays, grown plants are not so apparently affected ; 
the plant tissues seem to have some power of correction, and so the 
difference in the effects of the symmetry of the rays in the north 
as compared with the southern hemisphere is not observed. 
The symmetry of animals is of various kinds. The spherical kind 
is illustrated in the Protozoa. The Radiolaria, with their rays and 
their trellis work, show us what was, or is, being done, and raise inquiry 
as to the various agents that may be at work in bringing about 
the result. Still water or some inert fluid may be looked upon as 
favouring the maintenance of the spherical form seen in the resting 
stages of many Protozoa, but the surface tension may also contribute 
largely to the result. The sea anemones, simple sponges, and corals are 
admirable examples of the modified cylindric symmetry; the medusae 
illustrate the modified spherical symmetry. The mouth in the centre 
with appropriate radiating tubes, and in some cases the actual provision 
of separate segments with a definite nervous system, shows a very 
important departure in the bearings of the symmetry of a body on its 
life. The welfare of many an animal is so much connected with its 
colonial habits that its separation often means rapid extinction. The 
chance of extinction is diminished by the segmentation in question. 
Each part is, in a manner, independent of its neighbours; so are the 
parts of a star-fish, which may live after separation. A single ray may 
even turn over. A mechanical advantage seems also to be derived from 
a pair of fixed planes placed at right angles to one another, both as 
regards purchase and security, in the case of certain medusoids. The 
rhythm of Lhizostoma seems independent of the symmetry, 20 to 24 
contractions per minute in a closed vessel were noted in one case. The 
rhythm is best counted in the sea, however, an operation which is only 
possible there in some medusae. The motion of the fiuid from centre 
