22 Allgemeine Biologie und Entwickelungslehre. 



was absent in the parents. The general conclusion is that the theoretical 

 "purity of the gametes" does not exist, nor is there a "purity of factors". 



Haacke publishes an extensive account of breeding experiments with Mus, 

 dealing with coat-color, waltzing character, etc. The results throughout are 

 held to be in strict accord with Mendelian principles, though the work was 

 carried out without previous knowledge of Mendel's laws. 



Doncaster( 2 ) contributes data on inheritance of coat color in Mus decuma- 

 nus. Two types of albino individuals are found to exist here as in mice. 



Dealing with the inheritance of polydactylism Castle( 2 ) traces the history 

 of a polydactylous race of Cavia which he has bred. The normal C. has 4 

 toes on each of the front feet and only 3 on each of the hind feet. The 

 polydactylous race shows a four -toed condition of the hind feet. The race 

 sprung originally from a single cf four-toed ancestor. It is found that the 

 factor of gametic potency is more important than ancestry, for individuals 

 having the same amount of polydactylism in their ancestry differ widely in 

 their ability to transmit the polydactylous condition to their offspring. The 

 original ancestor of the race had the extra toe present on the left side only, 

 and in the progeny whenever an extra toe is present on one side only it is 

 more likely to be on the left than on the right side. Attempts to increase 

 this asymmetry by selection failed. The inheritance of polydactylism in this 

 case is found to be neither strictly alternative (Mendelian) nor blending, but 

 in a manner intermediate between the two methods. There occurs a partial 

 blending of the gametes in the zygote and a partial segregation as the zygote 

 gives off gametes. 



Castle & Forbes discuss the inheritance of hair length in Cavia. Differ- 

 ent races of G. exhibit two distinct types of hair growth; one a determinate 

 growth in which the hair grows to a certain length and then stops, the follicle 

 degenerating and the hair being ultimately shed; the other an indeter- 

 minate growth, where the follicle remains active and the hair continues to 

 grow for an indefinite period. When short-haired animals are mated with 

 long-haired ones the short-haired condition is dominant, but the hair length of 

 the offspring is usually on the average somewhat greater than that of the 

 parents, though it falls within the range of variation of the latter. On mat- 

 ing such cross- breds together the original long-haired and short-haired condi- 

 tions both reappear in the offspring (in accord with Mendelian expectation) 

 and there is also a third offspring type in which the hair length is intermediate 

 between the short- and the long-haired condition- Experiments showed that 

 this intermediate condition represents a new character in inheritance formed by 

 an incomplete synthesis of the gametic characters representing the short- and 

 long-haired conditions respectively. The results indicate that in gametic coupl- 

 ing the gametes do not remain pure, but that the maternal and paternal 

 characters exert a mutual influence on one another to produce a new inter- 

 mediate type. 



Rommel & Phillips find that there is a sensible inheritance of fecundity 

 as measured by size of litter in Sits. The intensity of this inheritance dimi- 

 nishes with the age of the Q, but this "does not necessarily mean that the 

 inheritance of fecundity is lost as the sow grows older, but probably indicates 

 that inheritance from the dam gradually plays relatively less and less of a 

 part in the determination, while other factors, notably nutrition, play more". 



Rommel ( 2 ) presents extensive data on the fecundity of two domestic races 

 of Sus. In one race (Poland China) there has been a distinct increase in 

 fecundity during a period of twenty years. 



