182 SUMMARY OF CUKKENT RESEAKCHES RELATING TO 



for the most part more tail feathers than has the common pigeon, 

 but less than the fantail." In the F^ generation the 12-feather tail 

 reappeared in considerable numbers ; the " curve " is at least bimodal 

 with one apex in the 14, 15, 16 rows, and the other in the 12 row ; a 

 few individuals approached the lower range of variation of the fantail, 

 viz. those with 24, 25 and 26 tail feathers. It is probable that a gene 

 for more than 12 feathers, and the gene for no oil gland, and a gene for 

 white colour are linked, i.e. are.carried by the same chromosome. 



Sex-ratio in Domestic Fowl.* — Raymond Pearl considers data 

 representing 22,000 chicks. The ratio of males per 1000 females is 

 944, or 48 • 57 p.C-, and it is interesting to notice that Darwin's figure 

 was 48 * 64. There is variability from stock to stock and from year to 

 year. Before aberrant sex-ratios can be considered indicative either of 

 environmental or hereditary effects, it is necessary to show that they 

 occur with such frequency as to exceed considerably that expected on 

 the basis of chance alone. Prenatal mortality in the fowl is not differen- 

 tial in respect to sex, and in consequence the observed sex-ratio at birth 

 is to be regarded as substantially the same as the initial zygotic sex- 

 ratio. 



b. Histolog-y. 



Shape of Red Blood-corpuscle in Mammals.t — L. B. Arey has 

 made a series of experiments to solve the much-disputed problem of the 

 normal shape of the red blood-corpuscle in mammals. He discusses the 

 evidence derived from (1) drawn blood, (2) circulating blood, and (3) 

 fixed tissues or smears, by other investigators, and supplemented by his 

 own experiments. He finds that the shape of the mammalian red blood- 

 corpuscle depends largely on the osmotic pressure of the examining 

 medium. In solutions corresponding to about ' 9 p.c. sodium chloride 

 the erythroplastid possesses a biconcave form. In progressively less 

 •concentrated (hypotonic) solutions water is imbibed, and the corpuscles 

 swell to thin-walled cups, thick-walled cups, dimpled spheres, and finally 

 lake-forming "shadows." In hypertonic solutions crenation results. 

 Between the limits of form induced by a 0'3 p.c. sodium chloride 

 solution and by mild crenation the shape of the red blood-corpuscle is 

 repeatedly reversible. Individual variability exists in the response of 

 erythroplastids to diluting media ; this is perhaps referable to diverse 

 elasticities of the corpuscular membranes. Undiluted drawn blood and 

 blood diluted with human serum show the corpuscles to be bi-concave 

 discs. Human serum must be diluted about one-third with water before 

 cups begin to form. The study of circulating-blood in non-ansesthetized 

 living mammals corroborates the view of the normality of the disc. The 

 results gained by the use of fixatives, although seemingly adverse to the 

 disc view, can be satisfactorily interpreted in terms of unequal fixation ; 

 this is supported by experiment. The several lines of experiment seem 

 to justify the conclusion that the bi-concave disc represents the normal 



* Proc. Amer. Phil. Soc, Ivi. (1917) pp. 416-36 (3 figs.), 

 t Amer. Journ. Anat., xxii. (1917) pp. 440-74 (1 fig.). 



