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22 the other. Such parallel investigations would also increase our knowledge as to the most suitable media and quantities of the extracts. It is also to be desired, from the theoretical point of view, that knowledge may be gained as to whether the internal secretion of the genital glands enters into chemical union with the protoplasm of the cells or whether it acts as a physiological stimulus independent of the quantity supplied. So far we know nothing that would enable us to come to a definite opinion on this point.

The limited influence of the internal secretions of the sexual glands in forming the sexual characters must be realised to warrant the theory of a primary, generally slight, difference in each cell, but still determinate sexual influence. If the existence of distinct graduations of these primary characteristics in all the cells and tissues can be recognised, there follow many important and far-reaching conclusions. The individual egg-cells and spermatozoa may be found to possess different degrees of maleness and femaleness, not only in different individuals, but in the ovaries and testes of the same individual, especially at different times; for instance, the spermatozoa differ in size and activity. We are still quite ignorant on these matters, as no one has worked on the requisite lines.

It is extremely interesting to recall in this connection that many times different investigators have observed in the testes of amphibia not only the different stages in the development of spermatozoa, but mature eggs. This interpretation of the observations was at first disputed, and it was suggested that the presence of unusually large cells in the tubes of the testes had given rise to the error, but the matter has now been fully confirmed. Moreover, in these Amphibia, sexually intermediate conditions are very common, and this should lead us to be careful in making statements as to the uniform presence of arrhenoplasm or thelyplasm in a body. The methods of assigning sex to a new-born