1018] on Gamete and Zygote 2;i7 



produced by the zygote. If the gametes uniting in fertilization are 

 identical in composition, those subsequently formed by the zygote 

 will be like them, save in the rare and exceptional case of new and 

 original variation. The divisions by which such cells are formed are 

 divisions of equality or repetition. If the combining gametes were 

 unlike, sooner or later in the germ-cell lineage divisions of diversity 

 or differentiation must occur. Similarly in zygotic cells these two 

 kinds of division are familiar, and thus an imperfect but profitable 

 comparison may be instituted between the differentiating divisions 

 by which the bodily organs are marked off, and those by which the 

 dissimilar properties of the series of gametes are distributed. All 

 permanence and all diversity are ultimately traceable to the process 

 of cell-division. 



The nuclei contributed by the father and by the mother com- 

 monly unite intimately, l)ut in Cyclops they lie in pairs, side by side, 

 in each cell throughout life. AVe have as yet no proof that recom- 

 binations of parental characters can occur in such a form as Cyclops, 

 but on analogy we can scarcely doubt that they may. Experiments 

 with such types might lead to discoveries as to nuclear functions. 



The sterility of hybrids is a consequence of the failure to sort out 

 or distribute the two sets of parental characters among the gametes. 



As to the physical nature of segregation there is still no light 

 whatever. Before we can form a conjecture regarding that process 

 some correct knowledge as to mechanism of ccill-di vision in general 

 must be obtained. The geometrical appearances and the phenomena 

 of polarity are the only available guides. No plausible representa- 

 tion of the physical process by which a cell divides into two equal 

 halves has been devised, but in view of the experiments of Loeb and 

 others showing that complete development may, in the case of the 

 frog's Qgg, be excited by the prick of a needle (as well as by other 

 stimuli), the conclusion is probable that fertilization acts by releasing 

 a strain. Divisions of equality may occur such that from the division 

 of the fertilized ovum two, four, six or more identical organisms 

 may be formed (twins ; quadruplets occurring normally in Armadillo, 

 etc.). More curious are the cases in which a yronp of meristematic 

 cells has the power of separating, developing axes, and becoming an 

 embryo (Crina, Harmer). We are here reminded of the observa- 

 tions of H. Y. Wilson (confirmed by J. Huxley) that if certain 

 sponges are pulped through a fine cloth, the separated cells can join 

 together and sort themselves into fresh orderly aggregations. 

 Compare also the fact that in Winkler's famous graft-hybrids in 

 Solanum, a peripheral tissue derived from one species can fit itself to 

 a core derived from another. Such facts plainly indicate that 

 powers of orderly adjustment are possessed by living things, but the 

 arguments of Driesch, that such powers are transcendental, seem 

 altogether premature, and may be dismissed as counsels of despair. 



The generalization may be hazarded that in somatic repetitions 



