We may consider it as established by the work of McClung, Sutton, E. B. Wilson, Miss Stevens, Morgan, and many others, that the chromosomes are the carriers of the Mendelian characters. These chromosomes occur in the nucleus of the egg and in the head of the sperm. Now the latter consists, in certain fish, of lipoids and a combination of nucleinic acid and protamine or histone, the latter a non-coagulable protein, more resembling a split product of one of the larger coagulable proteins. A. E. Taylor[57] found that if the spermatozoa of the salmon are injected into a rabbit, the blood of the animal acquires the power of causing cytolysis of salmon spermatozoa. When, however, the isolated protamines or nucleinic acid or the lipoids prepared from the same sperm were injected into a rabbit no results of this kind were observed. H. G. Wells more recently tested the relative efficiency of the constituents of the testes of the cod (which in addition to the constituents of the sperm contained the proteins of the testicle). From the testicle he prepared a histone (the protein body of the sperm nucleus), a sodium nucleinate, and from the sperm-free aqueous extract of the testicles a protein resembling albumin was separated by precipitation.[58] The albumin behaved like ordinary serum albumin or egg albumin, producing typical and fatal anaphylactic reactions and being specific when tried against mammalian sera. The nucleinate did not produce any reactions when guinea-pigs were given small sensitizing and larger intoxicating doses (0.1 gm.) in a three weeks’ interval; a result to be expected, since no protein is present in the preparation. The histone was so toxic that its anaphylactic properties could not be studied. [57] Taylor, A. E., _Jour. Biol. Chem._, 1908, v., 311. [58] Wells, H. G., _Jour. Infect. Diseases_, 1911, ix., 166. 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,[59] 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.