VARIATIONS IN ANIMALS AND PLANTS 493 



black. The ornithologists have not yet agreed on a subdivision of this 

 species into larger northern or smaller southern subspecies, nor have 

 the darker specimens from regions of greater rainfall received distinct 

 names. Similar variations have been noted in the Hudsonian chicka- 

 dee (Parus hudsonius) and in other birds of the northern forests. To 

 what extent the variations seemingly due to direct influence of climate 

 are hereditarv has not been ascertained. 



While the embryo may be deprived of its normal growth momentum, 

 the effect of unfavorable conditions is spent with a few generations of 

 normal life, and no direct change in the heredity of the race is known 

 to arise from the direct effects of environment. 



Food Variations of Silkworms 



Elaborate experiments in the effects of the underfeeding of silk- 

 worms have been made by Professor Vernon L. Kellogg and Mrs. 

 Ruby Green Smith. The following synopsis of the results is given 

 by Mrs. Smith. 



The effects of underfeeding (which have been studied in heredity) upon 

 the immediate generation fed on half the normal supply of food, may be classi- 

 fied as (1) physiological and as (2) those subject to quantitative measurement. 

 They are as follows: 



I. Physiological : 



1. Larval moltinga, pupation and emergence ot adult delayed and metamorphosis 



thereby prolonged. 



2. Fertility reduced (as indicated by number of eggs laid, number hatching and num- 



ber of individuals reaching maturity). 



3. Mortality in all stages greater than among normally-fed individuals. 



II. Variations from the normal which are subject to quantitative measure- 



ments. 



1. Reduction in size and weight of all parts in all stages (exemplified statistically and 



quantitatively by larval widths and lengths, by moth wing expanse, and by larval, 

 pupal and adult weights). 



2. Reduction in quantity of silk produced, the cocoons being below normal in dimen- 



sions, thickness and weight. 



3. Degeneration of wing veins slightly more marked than in normally-fed individuals 



(economy of material being practised to advantage in these comparatively useless 

 structures). 



The results of underfeeding in heredity have been studied in three genera- 

 tions derived from the original underfed great-grandparental stock. The char- 

 acters which the underfeeding was known to affect were studied in a compara- 

 tive way in 1904 among numerous lots. 



Heredity of underfeeding among silkworms whose make-up may be sum- 

 marized as follows: 



1. Lots accustomed always to years of plenty. 



2. Lota in which some one of the four generations experienced famine 



3. Lots in which famine was experienced in two alternate or two successive years. 



4. Lots in which famine was experienced in three successive or in one alternate and 



two successive years. 



Conclusions. 

 Throughout these lots the conclusions were consistent, and were in brief 

 as follows: 



1. The lingering eflects of a single generation of underfeeding may be definitely traced 

 to the third generation, although the progeny of the underfed generation be given 

 the optimum amount of food. 



