September 25, 1919] 



NATURE 



81 



further research. (2) It is desirable to obtain accurate 

 positions and proper motions of as many stars as 

 possible of types M and N. Owing to their non- 

 actinic .colour, these stars are more suitable for visual 

 than for photographic research. 



HEREDITY AND EVOLUTION. 



T N recent investigations on the subject of heredity 

 ■*■ much interest has centred around the question of 

 the determination of sex. In this connection attention 

 may be directed to a short but important paper by 

 Prof. Jacques Loeb (Proc. Nat. Acad. Sci., Washing- 

 ton, vol. iv., 1918, pp. 60-2), in which he describes 

 observations on the sex of frogs developed from 

 parthenogenetic eggs incited to segmentation by the 

 mechanical stimulus of puncture. Twenty of these 

 creatures reached ages of from ten to eighteen months, 

 several attaining the size of the full-grown, normal 

 adult male, to which sex belonged seven of the nine 

 the gonads of which were examined, the other two 

 being females. Hence it appears that frogs of either 

 sex niay arise as the result of "artificial partheno- 

 genesis." Cytological study demonstrated the presence 

 of the full (diploid) number of chromosomes in these 

 males, and Prof. Loeb infers that the female is 

 probably heterozygous for the sex-character. But 

 there seems to be good evidence for an "indifferent " 

 condition as to sex in some immature frogs at least, 

 as shown by the well-known researches of Prof. R. 

 Hertwig and suggested by observations of Prof. Loeb 

 in a former paper of his that the testes of a male 

 just after transformation may contain a few eggs. 

 It is doubtful, therefore, whether sex in frogs is 

 absolutely determined by the nature of the germ- 

 chromosomes. 



Individual animals in which the secondary charac- 

 ters of the two sexes are combined afford a curious 

 puzzle to students of this question. In the Journal 

 of Genetics (vol. vii.. No. 3) the Rev. J. E. Hull gives 

 details of a few cases of such " gynandry " among 

 spiders. In one case {CEdothorax fuscus) the speci- 

 men externally was " completely male on the left side 

 and female on the right " ; in another (Maso siin- 

 di'vallii) it was "male on the left side, but not quite 

 female on the right," the apex of the right palp being 

 somewhat swollen. A third spider {Lopho-mma herbi- 

 gj-aduiii) was perfectly male on the right of the 

 cephalothorax, with modified falx and palp, and 

 female on the left, but the abdomen showed the 

 characteristic female epigyne half-developed on the 

 right, the left half of the abdomen being male. Such 

 abnormalities, though highly interesting, are so rare 

 that it will probably be long before thev will vield 

 much enlightenment on fundamental problems of .sex. 

 In the same issue of the Journal of Genetics Mr. 

 D. \V. Cutler describes the spermatogenesis of infer- 

 tile hybrids between pheasant and Gold Campine 

 fowl, and finds that the process is abnormal: "The 

 failure of the synaptic threads to form bivalent 

 chromosomes is evidently the cause of sterility in the 

 hybrids." This result is compared with those derived 

 from the study of the germ-cells of other sterile 

 hybrids, in some of which the sex is apparently deter- 

 mined by the sex of one of the parent species. 



A short but noteworthy contribution to this subject 

 is Drs. L. J. Cole and W. A. Lippincott's paper en 

 the relation of plumage to ovarian condition in a 

 Barred Plvmouth Rock pullet (Biol. Bull., vol. xxxvi.. 

 No. 3). This bird assumed- partially the male 

 plumage, and the change was found to be due to a 

 large ovarian tumour; though the abnormal feathers 

 were like those of a male in shape and structure, they 

 resembled hen feathers as regards "barring." This, 



NO. 2604, VOL. 104] 



the authors believe, differentiates "secondary sexual 

 dimorphism from dimorphism caused through sex- 

 linkage as illustrated by the barring." After an 

 implantation of normal ovarian tissue, new feathers 

 which were definitely female grew in a few weeks. 



New subjects for hybridising experiments are 

 afforded by the northern and . southern forms of 

 African ostrich, the results of crossing which are 

 described by Prof. J. E. Duerden (Journal of 

 Genetics, vol. viii., No. 3). These two species (or sub- 

 species) interbreed freely, and the offspring are fertile 

 among themselves and with the parent forms. 

 " Everything points to the distinctive characteristics 

 of the two species as having separate factorial repre- 

 sentation in the germ plasm." The bald patch on the 

 head of the northern race is dominant to the feathered 

 condition of the southern, but in most features 

 "blended" inheritance is apparent. None of the 

 specific characters appear to have any adaptive value. 

 The application of Mendelian analysis to economic 

 plant-breeding is well exemplified by A. St. Clair 

 Caporn's studies (Journal of Genetics, 'vol. vii., No. 4) 

 on early and late ripening in an oat-cross and on 

 variation in glume-lengths of extracted parental tvpes 

 and the inheritance of purple colour in a wheat- 

 cross (Triticum polonicumxeloboni). " Earliness " 

 and "lateness" in oats are not sharply defined 

 characters ; they are spread over a period, though 

 "the ripening times of the parents used did not over- 

 lap." The hybrids were more or less intermediate, 

 while in the F, generation there was "evidence of 

 early, late, and many intermediate forms." Some 

 remarkable results were obtained from the wheat- 

 crossing experiments. In the F, generation a marked 

 change in the average length of the glumes in 

 homozygous long-glumed plants "as compared with 

 the average of the parent T. polonicum, under equal 

 conditions, persists right through into the F, genera- 

 tion." The inheritance of purple pericarp colour "is 

 distinguished by one cardinal and unaccounted for 

 anomaly; segregations analogous to the F. segrega- 

 tion have not been found in the Fj generation." 



Most students of " Mendelism " would probably 

 hold the opinion that little remains to be added to 

 our knowledge of the classical case of the blue .Anda- 

 lusian fowl But Dr. W. .\. Lippincott (Ame.r. Nat., 

 vol. Hi., No. 614) gives reasons for believing that 

 ' the 1:2:1 ratio is in reality a combination of two 

 3 : I ratios," and that the condition in the blues is 

 due to the combined action of two factors, one of 

 which restricts the distribution of the black pigment 

 within the feathers in such a way that it gives the 

 characteristic blue-grey appearance, while the other 

 extends the black pigment to every feather of the bird. 

 Somewhat similar suggestions had previously been 

 made by R. Goldschmidt and by A. L. and A. C. 

 Hagedoorn. According to Dr. Lippincott, the birds 

 usually defined as "white splashed with black" would 

 be more correctly described as "blue-splashed." His 

 theory seems largely dependent on the possibility of 

 "crossing-over" of determinants in the chromosomes, 

 for which no evidence is yet forthcoming, and he 

 admits that "if these cross-overs should not be found, 

 it might at first appear that the interpretation of the 

 case of the blue Andalusian is in all probability 

 exactly what has been suggested from the first, 

 namely, that blue is a heterozygote intermediate 

 between the parental types." 



.\ noteworthy critical discussion on the factors of 

 organic evolution has been contributed by Prof. L. B. 

 Walton to the American Naturalist (vol. lii. Nos. 622- 

 23). He believes that heritable characters in general 

 arise from preformed unit factors that may have 

 been in existence during long geological periods ; the 



