GENESIS. 283 



indifferent tissue; and in Tctliya, one of the sponges, Prof. 

 Huxley has observed that they occur mingled together in the 

 general parenchyma. The pollen-grains and embryo-cells of 

 plants arise in adjacent parts of the meristematic tissue of 

 the flower-bud ; and from the description of a monstrosity in 

 the Passion-flower, recently given by Mr. Salter to the Lin- 

 na^an Society, it appears both that ovules may, in their gen- 

 eral structure, graduate into anthers, and that they may 

 produce pollen in their interiors. Moreover, among the lower 

 Algce, which show the beginning of sexual differentiation, 

 the smaller gametes, which we must regard as incipient sperm- 

 cells, are sometimes able to fuse inter se, and give rise to a 

 zygote which will produce a new plant. All which evidence 

 is in perfect harmony with the foregoing conclusion; since, 

 if sperm-cells and germ-cells have natures not essentially un- 

 like those of unspecialized cells in general, their natures 

 cannot be essentially unlike each other. 



The next general fact to be noted is that these cells whose 

 union constitutes the essential act of gamogenesis, are cells 

 in which the developmental changes have come to a close — 

 cells which are incapable of further evolution. Though they 

 are not, as many cells are, unfitted for growth and meta- 

 morphosis by being highly specialized, yet they have lost the 

 power of growth and metamorphosis. They have severally 

 reached a state of equilibrium. And while the internal 

 balance of forces prevents a continuance of constructive 

 changes, it is readily overthrown by external destructive forces. 

 For it almost uniformly happens that sperm-cells and germ- 

 cells which are not brought in contact disappear. In a plant, 

 the egg-cell, if not fertilized, is absorbed or dissipated, while 

 the ovule aborts; and the unimpregnated ovum eventually 

 decomposes : save, indeed, in those types in which partheno- 

 genesis is a part of the normal cycle. 



Such being the, characters of these cells, and such being 

 their fates if kept apart, we have now to observe what 

 happens when they are united. In plants the extremity 



