486 MISSES K. FOOT AND E. C. STROBELL : 



for the other two exclusively male characters — the genital spot and the- 

 intromittent organ. These three exclusively male characters — the genital 

 spot, the intromittent organ, and the testis — can therefore, according to the 

 hypothesis, be transmitted by the female-producing spermatozoon as well as 

 by the male-producing spermatozoon. 



The defenders of the chromosome-hypothesis of sex-determination would 

 have us ignore these facts. Morgan ('14) says : — " To assume that all the- 

 factors for characters that are shown by the male or by the female must be 

 carried by a sex-chromosome of some kind, if carried at all by chromosomes,, 

 is a travesty of the point of view of those who hold to the chromosome- 

 hypothesis as a reasonable working hypothesis to account for Mendelian 

 inheritance." This sounds like an effort to evade the force of the real facts. 

 It should be added that two of these " characters "" (the intromittent organ 

 and the testis) are so exclusively male that without them the insect would 

 not be a male, and to present these facts and the conclusions which they 

 logically involve can scarcely be called "a travesty" of the hypothesis. 

 that asserts that factors determining sex are carried and distributed by 

 " sex-chromosomes ." Rather it is a serious and perfectly logical challenge 

 of some recent extreme views as to the function of the chromosomes in. 

 heredity. 



Oxford, March 1915. 



References. 



Bridges, Calvin B. 



'13. Non-disjunction of the Sex Chromosomes of Drosophila. Journ.. 

 Exper. Zool. vol. xv. No. 4. 

 Castle, W. E. 



'11. Heredity in Relation to Evolution and Animal Breeding.' 



D. Appleton & Company. 1911. 

 '12a. The The Inconstancy of Unit-characters. Amer. Nat. vol. xlvi. 

 '12 h. Some Biological Principles of Animal Breeding. Amer. Breeders' 



Magazine, vol. iii. No. 4. 

 '14 a. Multiple Factors in Heredity. Science, n. s. vol. xxxix. 

 ""14 6. Pure Lines and Selection. Journ. of Heredity (Organ of the 

 Amer. Genetic Assoc), Washington, D.C., vol. v. No. 3. 

 Castle, W. E., and John C. Phillips, 



■'lie. Piebald Rats and Selection. An experimental test of the effect- 

 iveness of selection and of the theory of gametic purity in 

 Mendelian crosses. Carnegie Institution of Washington, 1914. 

 Darwin, Charles Robert. 



'59. The Origin of Species. 1859. 

 '86. The Descent of Man. 1886. 



