Chromatin as '^Hereditary Substance'' .353 



gall flies and phjUoxerans.* And observations have lately 

 been published which strongly indicate the dependence of 

 sex upon chromosomes in other animals in which partheno- 

 genesis and hermaphroditism occur. This is notably true 

 of aphids, certain nematode worms, and a pteropod mol- 

 lusc. Summing up, we may say, then, tliat in a considerable 

 number of animals sex is proved to be hereditary and to be 

 connected with the chromosomal condition of the germ- 

 cells. 



The Con/nection of Mutation with Particular Chromosomes 



Finally, the most surprising evidence in favor of the 

 theory that chromosomes are bearers of heredity, is the dis- 

 covery that certain attributes in some animals and plants, 

 not necessarily peculiar to either one sex or the other, but 

 which arise as mutations and are transmitted in Mendelian 

 fashion, are connected with particular chromosomes. The 

 best investigated examples are furnished by the evening 

 primroses, plants which have become famous in connection 

 with the mutation theory. 



Mr. R. Ruggles Gates, one of the foremost workers in this 

 specialty, has lately epitomized the facts and views held rela- 

 tive to the chromosomal characters of plants. He writes 



* The investigators who have contrihuted most to the descriptions of 

 the chromosomal conditions of the honey bee are J. F. Meves {Die 

 SpermatocytenfeUunf/en bei der Honlghiene, Arch. f. Mikr. Anat. Bd. 70, 

 p. 414, 1907) and H. Nachtsheim, referred to above. Meves and J. 

 Deusberg {Die Spermaiort/fenfeiiimf/en bei der Ilornisse. Arch, fiir 

 Mikr. Anat. Bd. 71, 1908) have investigated the wasp. The gall flies 

 have been studied by L. Doncaster. {Gameto gene sis of the Gall fly 

 Neuropterus LEXTicrLARis Proc. Roy. Soc. B. 82, 1910, p. 88 and B. 83, 

 1911, p. 476.) The germ-cells of certain Phylloxerans have 

 been the subject during the last ten years of some of T. H. Morgan's 

 most important studies. His first paper, {The Male and Female Eggs 

 of Phylloxerans of the Hickones, Biol. Bull. Vol. 10, p. 210) was 

 published in 190fi. In all he has written something like a dozen 

 papers on the subject, the last so far as I know having appeared in 1915 

 {The Predetermination of Sex in Phylloxerans and Aphids. Jour. Exper. 

 Zool. Vol. 19, Oct. 1915, p. 285). 



