SCIENCE 



[N. S. Vol. XXVII. No. 681 



eharaeteristie organs to whicli they give rise 

 appear in these same abnormal positions. 

 There is, therefore, in this case, both nega- 

 tive and positive proof that these materials 

 of the cytoplasm of the egg are actually 

 ' ' organ-forming substances. ' ' 



5. In diiferent phyla there are marked 

 differences in the localization of the oo- 

 plasmic substances, corresponding to differ- 

 ences in the location of the organs in the 

 embryo or larva. Many different phyla 

 may, therefore, be distinguished by the 

 type of ooplasmic localization which they 

 show. In its general features, therefore, 

 the characteristics of the phylum are pres- 

 ent in the cytoplasm of the egg cell. 



All of these observations on the cyto- 

 plasm go to show that it is not isotropic, 

 as Hertwig supposed, but that it is differ- 

 entiated and that many of the character- 

 istics of animals, especially such as apply 

 to their general type of organization, are 

 represented in the cytoplasm of the egg. 



6. Finally as evidence that inheritance 

 may take place through the cytoplasm of 

 the egg, reference must be made to the ex- 

 tremely important work of Loeb and of 

 Godlewski. By concentration of hydroxyl 

 ions Loeb found that it was possible to 

 cause the spermatozoa of -starfishes and 

 ophiurans to fertilize the eggs of sea ur- 

 chins. The embryos and larvae resulting 

 from such crosses showed only the char- 

 acteristics of the mother. Later Godlewski, 

 using the same methods, was able to fertilize 

 the eggs of a sea urchin by the sperm of a 

 crinoid," and although such hybrids were 

 raise^d to the larval stage they showed only 

 maternal characteristics. Still more, enu.- 

 cleated urchin eggs fertilized by crinoid 

 sperm produced gastrulse of purely urchin 

 type. These results demonstrate, as Boveri 

 admits, that the chromosomes of the sperm 

 do not in this case influence or modify the 

 cytoplasm of the egg cell ; while the experi- 

 ments on the enucleated egg show that the 



characteristics of the organism, at least as 

 late as the gastrula stage, are derived en- 

 tirely from the egg cytoplasm. 



Boveri long since showed that the early 

 stages of development, perhaps as late as 

 the blastula or gastrula, are iminfluenced 

 by the spermatozoon and are purely ma- 

 ternal in type; in the case of Godlewski 's 

 hybrid larvae he supposes that the sperm 

 chromosomes remain permanently inactive. 

 But however this result is to be explained, 

 it may be considered as definitely settled 

 that the early development of animals is 

 of purely maternal type, and that it is only 

 in stages later than the gastrula, and con- 

 sequently after the broad outlines of devel- 

 opment and the general type of differen- 

 tiation have been established, that the influ- 

 ence of the spermatozoon begins to make 

 itself felt; and it is equally certain that 

 this type of differentiation is predetermined 

 in the cytoplasm of the mature egg cell, 

 rather than in the egg nucleus. 



On the other hand, there is no doubt that 

 the differentiations of the egg cytoplasm 

 have arisen, in the main, during the ovarian 

 history of the egg, and as a result of the 

 interaction of nucleus and cytoplasm; but 

 the fact remains that at the time of fertil- 

 ization the hereditary potencies of the ttvo 

 germ cells are not equal, all the early devel- 

 opment, including the polarity, symmetry, 

 type of cleavage, and the relative positions 

 and proportions of future organs ieing pre- 

 determined in the cytoplasm of the egg cell, 

 while only the differentiations of later de- 

 velopment are influenced hy the sperm,. 

 In short, the egg cytoplasm fixes the type 

 of development and the sperm and egg 

 nuclei supply only the details. 



This conclusion is not a refutation of 

 the nuclear inheritance theory, but it is a 

 profound modification of it. At once it 

 destroys the argument that since there is 

 equality of inheritance from both parents 

 there must be equivalence of inheritance 



