CRITICISM 65 



4. Hickson (1907) has argued forcibly in support of the view that 

 " for the present at any rate we can only say that the germ-cells as a 

 whole, and not any special part, are responsible for the transmission of 

 heritable characters from, generation to generation." He suggests 

 speculatively that the more plastic characters may be transmitted 

 mainly by the cytoplasm and the rigid characters by the nucleus. 

 In his criticism he refers to cases where chromosomes are quite 

 indistinct in the gametes, to the importance of cytoplasm-fusion in 

 the conjugation of some Protozoa, to the experiments of Herbst and 

 Fischel on hybridisation in Echinoderms, which indicate the im- 

 portance of the cytoplasm of the ovum in transmitting characters, 

 and to other sets of facts which indicate the danger of exaggerating 

 the importance of the chromosomes. The observations of Godlewski 

 are also strongly suggestive of the importance of the cytoplasm, as 

 well as the nucleus, in inheritance. 



5. Batcson (1907) has pointed out that if the chromosomes were 

 the bearers of hereditary characters, we should expect some degree of 

 correspondence between the differences distinguishing the types and 

 the visible differences of number or shape distinguishing the chro- 

 mosomes. Moreover, if the chromosomes were the chief governors 

 of structure we should expect to find greater differences between 

 them in different tissues of the same body. 



6. No one has protested more clearly and vigorously than Guyer 

 (1909, 1911) against "the inordinate importance which has been 

 attributed to the chromosomes as vehicles of heredity." He points 

 out, for instance, that there is definite experimental evidence of the 

 great importance of the ovum-cytoplasm, and argues that "the 

 number and arrangement of the chromosomes in a given species are 

 the effects of the fundamental constitution of a given kind of living 

 matter, rather than that they stand in a specifically causal relation 

 to such constitution." " Heredity is the problem of the handing-on 

 of metabolic energies already established, rather than of the transmis- 

 sion of a series of determinative units which create a wholly new 

 organism." " This much is certain : no chemical, physiological, or 

 morphological evidence is yet extant which places the hereditary 

 factors wholly within the chromosomes." It seems highly probable 

 that the chromosomes " control the velocities in cell-chemistry " by 

 supplying the proper amounts and kinds of ferments which act on a 

 series of fundamental cell-constituents that are largely common to 

 both egg and sperm. 



Perhaps then the safest conclusion at present is that the chromo- 

 somes, along with other germ-cell constituents, " stand in some definite 

 causal relation to adult characters." 



