512 



THE AMERICAN NATURALIST [Vol. XLIV 



would give rise to qualitative changes, in case the chromosome 

 should drop out. I have pointed out elsewhere 6 that in order 

 to explain Mendelian phenomena on the basis of the behavior of 

 chromosomes in the reduction division, it is not necessary to 

 assume in the chromosome definite pangenes or determinants as 

 separate entities. Each chromosome may take part in all phases 

 of development. It is hardly probable that any particular chro- 

 mosome, with the possible exception of a few of them, possesses 

 exclusively characteristics necessary to the continued existence 

 of the race in which they occur. In other words, speaking in a 

 general way, each of the chromosomes may possess all the meta- 

 bolic powers necessary to the race, while at the same time each 

 chromosome may differ from others in minor particulars, giving 

 rise to such differences as we see in Mendelian character pairs. 



The writer does not quite follow Guyer in doubting the ade- 

 quacy of the above interpretation of Mendelian phenomena, be- 

 cause in a few instances inheritance of a different type has ap- 

 parently been found, but he does agree with him when he says : 



There are no sufficient reasons, I think, why we may not look upon 

 their (the chromosomes') differences as differences of mere elemental, 

 chemical and physical constitution rather than as differences among 

 systems of determinate morphological units. . . . Even in case of the 

 divorcement of particular parental chromosomes in gametes ... it 

 would seem that we might account for the so-called Mendelian phe- 

 nomena by attributing to the chromosomes simply chemical ami pliy-- 



Guyer points out that because the three elements carbon, 

 oxygen and hydrogen condition substances of which they are 

 components, we do not postulate a specifically determinative 

 substance in any of them for each of the numerous carbohy- 

 drates and other products that result from their various com- 

 binations and arrangements. Similarly, we do not need to infer 

 definite structural elements in the chromosomes, each of which 

 is specifically determinative of a given character. It would seem 

 more logical to assume that the differences between related organ- 

 isms may be due to differences in the combinations of metabolic 

 activities found in the various cell organs. 



This paper of Guyer 's accords very closely with the teleone 

 theory of heredity propounded by the writer in the April num- 

 ber of the American Naturalist, 1910. It is gratifying to see 

 that a number of biologists are coming to the view that the 

 main facts of heredity can be explained without the assumption 

 of any hypothetical units in the germ plasm. W. J. Spillman. 



•American Naturalist, April, 1910. 



