It appears as a case of adaptation that the eggs of the majority of animals cannot develop without a spermato­zoön, and yet we can imitate the activating effect of a spermato­zoön on the egg by definite chemical compounds, which leads to the sugges­tion that the activating effect of the spermato­zoön on the egg might be due to the fact that it carries such a compound.

The wonderful adaptations exhibited in the mating instincts seem to be due to definite substances secreted by the sex glands, as was shown by Steinach (Chapter VII). Here, again, the process as popularly conceived, is the reverse of the truth; those survive that have the equipment,—they did not acquire the equipment under the influence of environ­ment.

It is absolutely imperative for green plants that their stems and leaves be exposed to the light since only in this way are they able to form carbohydrates; and it is equally essential that the roots should grow into the soil so that the plant may get the nitrates and phosphates required to build up its proteins and nucleins. This result is, in the language of adapta­tionists, brought about by an adaptive response of the plant to the light. In reality this adaptive response is due (Chapter X) to the presence of a photo­sensitive substance present in almost all green plants.

Lewis has shown that if the optic cup is transplanted under the skin of a young larva into any part of the body the skin in contact with the optic cup will form a lens; it looks as if a chemical substance from the optic cup were responsible for the forma­tion of the lens.

These examples might be multiplied indefinitely. They all indicate that apparent morpho­logical and instinctive adapta­tions are merely caused by chemical substances formed in the organism and that there is no reason for postulating the inheritance of acquired characters. We must not forget that there are just as many cases where chemical substances circulating in the body lead to indifferent or harmful results. As an example of the first type, we may mention the existence of helio­tropism in animals living in the dark, of the latter type, the inheritance of deficiencies like colour-blindness or glaucoma.

While it is possible for forms with moderate disharmonies to survive, those with gross disharmonies cannot exist and we are not reminded of their possible existence. As a consequence the cases of apparent adapta­tion prevail in nature.

The following observa­tion may serve to give an idea how small is the number of existing or durable forms compared with the number of forms incapable of existence. We have mentioned the fact observed by Moenkhouse, the writer, and Newman, that it is possible to fertilize the eggs of each marine bony fish with the sperm of practically every other marine bony fish. The number of teleosts at present in existence is about ten thousand. If we accomplish all possible hybridiza­tions, one hundred million different crosses will result. Of these only a small fraction of one per cent. can live (see Chapter I), and it is generally the lack of a proper circula­tion which inhibits them from reaching maturity. It is, therefore, no exaggera­tion to state that the number of species existing today is only an extremely small fraction of those which can and possibly do originate, but which escape our notice and disappear because they cannot live or reproduce. If we consider these facts we realize that the mere laws of chance are adequate to account for the fact of the apparently purposeful adapta­tions; as they are adequate to account for the Mendelian numbers.