560 SUMMARY OF CURRENT RESEARCHES RELATING TO 



When normal Amphibians were used, blue light was the most 

 effective in the production of tropic responses, but when eyeless 

 individuals were tested with the same coloured lights, the rays towards 

 the blue end of the spectrum showed no such potency as those near the 

 opposite end. It may be said that while both skin and eyes are sensi- 

 tive to the whole range of the visible spectrum, colour-sensitiveness is 

 present only in the latter. It is possible, however, that the supposed 

 colour-sensitiveness is due to the effects of what are intensity-differences 

 to the Amphibian eye. A decrease in the intensity of light brings about 

 a correspondingly smaller number of positively phototropic responses, 

 and an increase in the number of indifferent reactions. The phototropic 

 responses of eyeless toads are not due to the stimulation of heat- 

 receiving organs in the skin. Thermo- and photo-reception are separ- 

 ate processes, and the former does not readily give rise to tropic ' 

 reactions. " Spinal " Amphibians — in which the cord is severed from 

 the brain — gave no photic responses, but such reactions were induced in 

 animals in which the brain anterior to the metencephalon had been 

 excised. 



Cumulative Effect of Selection.* — R. Pearl and P. M. Surface 

 examine the results gained during the course of eleven years' experi- 

 menting with poultry, with a view to determining whether these indi- 

 cate that there is a cumulative effect of selection. The data discussed 

 were obtained from two lines of work. On the first of these, hens were 

 selected throughout a period of nine years for high egg production. 

 No hens were used as breeders whose production in the pullet year had 

 not been 160 or more eggs. The cockerels used were, after the first 

 year of the experiment, invariably the sons of mothers producing 200 or 

 more eggs in their pullet year. Secondly, the inheritance of egg pro- 

 duction from mother to daughter was directly measured. Records of 

 the pullet year of egg production of 250 daughters of hens, laying 200 

 or more eggs in their (the mothers') pullet year, were obtained. It was 

 found that selection for high egg production throughout nine years did 

 not sensibly increase the average production of the flocks, or lead to any 

 decrease in the variability of egg production. The data give no 

 evidence that there is a sensible correlation between mother and daughter 

 in regard to egg production, or that fecundity is sensibly inherited. The 

 daughters of the " 200-egg " hens did not exhibit, when kept under the 

 same environmental conditions, such a high average of egg production 

 as did pullets of the same age which were the daughters of birds whose 

 production was less than 200 eggs per year. The daughters of " 200- 

 egg " hens were not less variable in respect to egg production than were 

 similar birds whose mothers were not i o closely selected. 



In general, the authors are strongly inclined to the view that the 

 existing evidence indicates that the superior egg-production of present- 

 day races of domestic poultry is, in the main, the result of the action of 

 the favourable environmental conditions included in the process of 

 domestication rather than the effect of the selection of favourable 

 fluctuating variations through a long period of time. 



* Zeitscbr. Iuclukt. Abstammungs mid Vererbungslebre, ii. (190'J) pp. 257-75. 



