362 PRESEIsiT PROBLEMS IN EVOLUTION AND HEREDITY. 



vibratile form for its function of reaching and penetrating the ovum. 

 Tiie evidence of the Infusoria is paralleled among some of the plants, 

 in which conjugation between entirely similar cells is observed. 



The causes finally determining sex may come .surprisingly late in 

 development, and according to the investigations of Diising and the 

 exj)eriments of Yung* and of Giron are directly related to nutrition. 

 High feeding favors an increase of the percentage of females, while, 

 ccmversely, low feeding increases the males. In Yung's exi)eriments 

 with tadpoles the following results were obtained: 



Females. 



Males. 



Normal percentage 57 



High uutrition 92 



Geddes expresses this princii)le in physiological terms of metabolism, 

 that anabolic (constructive) conditions produce females, while katabojic 

 (destructive) conditions produce males. 



I think we may now safely eliminate the factor of sex from our cal- 

 culations u])on the problem of heredity, and thus rid ourselves of one 

 of the oldest and most widespread fallacies. We shall thus, in using 

 the terms "i)aternar' and 'maternal" imply merely the distinction 

 between two lines of family descent. 



The theory of reduction. — This leads us back to the significance of 

 the polar bodies. Van Benedeu's discovery that these bodies con- 

 tained chromatin led gradually to the view that they were not frag- 

 ments of the ova, but represented minute, morphologically complete 

 cells, liiltschli showed that they were given oif independently of, and 

 prior to, the contact of the spermatozoon, and, finding in the leeches 

 that the first polar body subdivides to form two bodies, ho considered 

 them as tormed by true cell division, and containing both nucleoplasm 

 and cliromatin. Giard indei)endently reached a similar opinion, as- 

 signing an atavistic meaning to tlie pohir cells. Wiutman, in 1878, 

 advanced the idea that they represented vestiges of the primitive 

 mode of reproduction by fission, while Mark described them as "abor- 

 tive ova," 



At this point speculation subsided until it was revived by Weis- 

 manii's attempt to connect these bodies with his theory of heredity,! 

 already referred to. The whole history is clearly given in E. Hert- 

 wig\s masterly memoir upon Ovo and Spermatogenesis in the Nema- 

 todes.! Taking advantage of Boveri's discoveries in staining tech- 



*' See Geddes aud Thomson: 'ihe EvoJni'wn of Sex, 1891; also, Diising: Die Regu- 

 lierung des GescLleclitsverliJIltnisses bei d. Vei'iiielirinig der Meiischen, Tiere iind 

 Pllauzen, Jen. Zelt. f. Natur., Bd. 17, 1884. 



t On the Number of Polar Bodies anl their Si^niticance in Heredity, 1887. 



tEi und Samenbilduiig bei Nem.todeii, Archie, f. Alikr, Anai., Bd. 26, 1890. 



