It is not impossible that protamines and histones might be found to act as specific antigens if they were not so toxic. The positive results which Taylor observed after injection of the sperm might have been due to the proteins contained in the tail of the spermatozoa, which in certain animals at least does not enter the egg and hence can have no influence on heredity.

It is thus doubtful whether or not any of the constituents of the nucleus contribute to the determination of the species. This in its ultimate consequences might lead to the idea that the Mendelian characters which are equally transmitted by egg and spermatozoön, determine the individual or variety heredity, but not the genus or species heredity. It is, in our present state of knowledge, impossible to cause a spermatozoön to develop into an embryo,' while we can induce the egg to develop into an embryo without a spermatozoön. This may mean that the protoplasm of the egg is the future embryo, while the chromosomes of both egg and sperm nuclei furnish only the individual characters.

1 Loeb, J., and Bancroft, F. W., Jour. Exper. Zoöl., 1912, xii., 381.

CHAPTER IV

SPECIFICITY IN FERTILIZATION

I. We have become acquainted with two characteristics of living matter: the specificity due to the specific proteins characteristic for each genus and possibly species and the synthesis of living matter from the split products of their main constituents instead of from a supersaturated solution of their own substance, as is the case in crystals. We are about to discuss in this and the next chapter a third characteristic, namely, the phenomenon of fertilization. While this is not found in all organisms it is found in an overwhelming majority and especially the higher organisms, and of all the mysteries of animated nature that of fertilization and sex seems to be the most captivating, to judge from the space it occupies in folklore, theology, and "literature." Bacteria, when furnished the proper nutritive medium, will synthetize the specific material of their own body, will grow and divide, and this process will be repeated indefinitely as long as the food lasts and the temperature and other outside conditions are

normal. It is purely due to limitation of food that bacteria or certain species of them do not cover the whole planet. But, as every layman knows, the majority of organisms grow only to a certain size, then die, and the propagation takes place through sex cells or gametes: a female cell-the egg-containing a large bulk of protoplasm (the future embryo) and reserve material; and the male cell which in the case of the spermatozoon contains only nuclear material and no cytoplasmic material except that contained in the tail which in some and possibly many species does not enter the egg. The male element-the spermatozoön-enters the female gamete the egg-and this starts the development. In the case of most animals the egg cannot develop unless the spermatozoön enters. The question arises: How does the spermatozoön activate the egg? And also how does it happen that the spermatozoon enters the egg? We will first consider the latter question. These problems can be answered best from experiments on forms in which the egg and the sperm are fertilized in sea water. Many marine animals, from fishes down to lower forms, shed their eggs and sperm into the sea water where the fertilization of the egg takes place, outside the body of the female.

The first phenomenon which strikes us in this connection is again a phenomenon of specificity. The spermatozoön can, as a rule, only enter an egg of the same or a closely related species, but not that of one more

distantly related. What is the character of this specificity? The writer was under the impression that a clue might be obtained if artificial means could be found by which the egg of one species might be fertilized with a distant species for which this egg is naturally immune. Such an experiment would mean that the lack of specificity had been compensated by the artificial means. It is well known that the egg of the sea urchin cannot as a rule be fertilized with the sperm. of a starfish in normal sea water. The writer tried whether this hybridization could not be accomplished provided the constitution of the sea water were changed. He succeeded in causing the fertilization of a large percentage of the eggs of the Californian sea urchin, Strongylocentrotus purpuratus, with the sperm of various starfish (e. g., Asterias ochracea) and Holothurians by slightly raising the alkalinity of the sea water, through the addition of some base (NaOH or tetraethylammoniumhydroxide or various amines), the optimum being reached when 0.6 c.c. N/10 NaOH is added to 50 c.c. of sea water. It is a peculiar fact that this solution is efficient only if both egg and sperm are together in the hyperalkaline sea water. If the eggs and sperm are treated separately with the hyperalkaline sea water and are then brought together in normal sea water no fertilization takes place as a rule, while with the same sperm and eggs the fertilization is successful again if both are mixed in the hyperalkaline solution. From

this the writer concluded that the fertilizing power depends on a rapidly reversible action of the alkali on the surface of the two gametes. It was found that

an increase of the concentration of calcium in the sea water also favoured the entrance of the Asterias sperm into the egg of purpuratus; and that if CCa was increased it was not necessary to add as much NaOH.

The spermatozoon enters the egg through the socalled fertilization cone, i. e., a protoplasmic process comparable to the pseudopodium of an amoeboid cell. The analogy of the process of phagocytosis-i. e., the taking up of particles by an amoeboid cell-and that of the engulfing of the spermatozoön by the egg presents itself. We do not know definitely the nature of the forces which act in the case of phagocytosis-although surface tension forces and agglutination have been suggested; both are surface phenomena and are rapidly reversible.

We should then say that the specificity in the process of fertilization consists in a peculiarity of the surface of the egg and spermatozoön which in the case of S. purpuratus and Asterias can be supplied by a slight increase in the COH or CCa.

By this method fifty per cent. or more of the eggs of purpuratus could be fertilized with the sperm of the starfish Asterias ochracea, capitata, Ophiurians, and Holothurians, while with the sperm of another starfish, Pycnopodia spuria, only five per cent., and with the