108 DIFFERENTIATION III 



3. Experiments on heterogeneous hybridization indicate 

 that it is the large characters those of the phylum, class, 

 order, family to which the animal belongs that are carried 

 by the cytoplasm, and, this means, transmitted through the 

 female germ-cell alone. 



4. At the same time the cytoplasm is, during pre-matura- 

 tion stages, indebted to the nucleus for certain elements in its 

 structure. In the female, therefore, these nuclear elements of 

 the cytoplasm are concerned in the transmission of inheritable 

 characters, as well as the chromosomes. 



5. In the chromosomes, the germ-cells of the two sexes are 

 alike, and these chromosomes are certainly concerned in the 

 transmission of some characters. 



6. It is known (a) by observation, (/3) by experiment that 

 there are qualitative differences between individual chromo- 

 somes, and that a complete set of these different chromosomes 

 must be possessed by every cell in the body if development is 

 to be normal. It is further probable that the chromosomes 

 themselves are heterogeneous. 



7. The different activities of the different chromatic elements 

 are probably only called forth by differences in their environ- 

 ment, that is, in the cytoplasm to which they are distributed. 

 It is known that differential behaviour of nuclei can be incited 

 by cytoplasmic dissimilarity. 



8. Hybridization experiments on nearly related forms make 

 it certain that the smaller characters generic, specific, varietal, 

 and individual can be transmitted as easily from the father 

 as from the mother, and therefore through the nuclei. 



II. THE INTERACTION or THE PARTS UPON 



ONE ANOTHER. 



The evidence discussed so far has taught us that the un- 

 developed egg possesses a structure, both in its cytoplasm 

 and in its nucleus, the parts of which are definitely related 

 to the formation of certain organs of the embryo. It does not, 

 however, follow that every separately inheritable character 



