536 SUMMARY OF CURRENT EESEARCHES RELATING TO" 



3. These points, together with the values for parental and grand- 

 parental correlations already given by Professor Pearson, make it 

 probable that the facts of inheritance of coat colour in horses can be 

 expressed in terms of the hypothesis outlined by Mr. Galton in 1872. 



Hurst replies to these objections. 



Heredity of Hair-length in Guinea-pig.* — W. E. Castle and 

 A. Forbes find that while long-haired and short-haired conditions are 

 sharply alternative to each other in heredity, the gametes formed by 

 cross breeds are not in all cases pure. Frequently they consist of a 

 blend or a mixture of the two alternative conditions, constituting in 

 effect a new condition intermediate between the other two. This is in 

 accordance with the results obtained for other characters, e.g. albinism, 

 alternative in heredity. It is concluded that gametic purity is not 

 absolute, even in sharply alternative inheritance. 



Origin of Polydactylous Race of Guinea-pigs.f — W. E. Castle, 

 having found that in guinea-pigs not infrequently a fourth digit, or 

 " extra toe," occurs on the hind limb, set himself the task of establishing 

 a race of four-toed examples. This was successfully accomplished from 

 the progeny of a single polydactylous individual, and the present paper 

 gives a detailed account of how it was done. It is evident from facts 

 submitted that the inheritance of the extra toe is not a case of simple 

 Mendelian dominance ; most polydactylous parents in mating with 

 normal individuals give a mixture of normal and polydactylous offspring, 

 rarely equal to each other in number — the expectation if one parent be 

 a Mendelian heterozygote and the other pure. There is, however, some 

 evidence of Mendelian segregation, and on the whole it seems probable 

 that the extra toe is inherited in a manner intermediate between blending 

 and alternative inheritance. 



Theory of Development.^ — W. Wedekind propounds a theory 

 according to which alternation of generations was universally the most 

 primitive form of ontogeny. By a process of constant abridgment 

 " metamorphosis " has arisen therefrom, and through continuous accelera- 

 tion of the ontogeny " direct development " has ensued from alternation 

 of generations and metamorphosis. " Direct development is everywhere 

 the secondary process, which, in consequence of its great rapidity, is 

 well nigh incomprehensible." This theory is briefly enunciated, and 

 the advantages and difficulties in the way of its acceptance are considered. 

 Further development in fuller detail is promised in connection with the 

 author's theory of parthenogenesis and determination of sex in higher 

 animals. 



Aortic Arches in Mammals.§ — F. T. Lewis has investigated in 

 particular the problem of the posterior aortic arches and the related 

 pharyngeal pouches in the rabbit and pig. The order of development 

 of the posterior part of the branchial system appears to be as follows : — 



* Carnegie Inst, of Washington Publications, No. 49 (1906) pp. 5-14. 

 t Tom. cit., pp. 17-29. 



% Zool. Anzeig., xxix. (1906) pp. 790-5. See also Ann. Mag. Nat. Hist., xviii. 

 (1906) pp. 38-44. 



§ Anat. Anzeig., xxviii. (1906) pp. 506-13 (2 figs.). 



