OPERATION OF THE GENETIC SYSTEM 8 1 



fertilization. In a later generation there are both males 

 and females. Many Rotifera are of this type. 



The relation to chromosomes of these diverse conditions 

 as to sex remains for the most part to be discovered. But 

 the great variety of conditions found among organisms 

 must be kept in mind, in order that the role of the chromo- 

 somes may not be misunderstood. They determine the sex 

 through the fact that they act chemically; they determine 

 It by altering the chemical conditions. Other things may al- 

 ter the chemical conditions too, and then these also may de- 

 termine sex. 



In general, the relations of chromosomes to sex, brought 

 out in the present chapter, demonstrate that the chromo- 

 somes affect development and characteristics through the 

 fact that they Influence the chemical materials and processes. 

 Other conditions may likewise Influence these processes, so 

 that the effects of chromosomes may be modified or nullified 

 by other conditions. 



NOTES AND REFERENCES ON CHAPTER m 



1. Page 55. Important general works on sex determination are: 

 E.Allen (Editor) (ig^l) , Sex and Internal Secretions, g^i pages; 



F. Schrader (1928), The Sex Chromosomes. Berlin, 194 pages; 

 R. B. Goldschmidt (1923), The Mechanism and Physiology of Sex 

 Determination. 259 pages; E. Witschi (1929), Bestimmung und 

 Vererbung des Geschlechts bet Tieren. Handbuch der Vererbungswis- 

 senschaft, Bd. II, Lieferung 10, 115 pages. 



2. Page 57. For an exhaustive account of the chromosomes in man, 

 with many figures, see H. M. Evans and O. Swezy (1929), The 

 Chromosomes in Man, Sex and Somatic. Memoirs of the University of 

 California, vol. 9, No. i, 65 pages, 11 plates. 



3. Page 59. See the following publications by C. B. Bridges: 

 (1916) Non-disjunction as a Proof of the Chromosome Theory of 



Heredity. Genetics, vol. i, pp. 1-52 and 107-163 ; (1922) The Origin 

 of Variations in Sexual and Sex-Limited Characters. American Nat- 

 uralist, vol. 66, pp. 51-63; (1932) "The Genetics of Sex in Dro- 

 sophila": in Allen's Sex and Internal Secretions, pp. 55-93. 



