15. That the sun is a perfect planet and hence must be made up of everything planetary can be seen from the fact that everything upon the planets is formed through the sun's radiating light. The difference between the perfect and imperfect planet can be seen only from the fact that all forms upon the latter arising from the light of the sun are necessarily determinate and not easily changeable and are even capable of counting; whereas upon the perfect solar planet, all forms are free and have no restriction other than the will of man, being therefore countless and infinitely different.
16. It can happen sometimes that even upon the imperfect planets through the effect of sunlight some more ancient species die out, whilst completely different ones come into being. But such cases on the planets are rare and the change and transition period requires a far lengthier period than upon the perfect sun-planet.