304 DARWINISM TO-DAY. 



moulting, during which time the so-called 'moulting fluid' is 

 secreted. That this effect may accumulate throughout the life- 

 time of the larva until the larva is actually forced to indulge in the 

 extravagance (of strength, feeding time, and body wall material) 

 of an additional moult is conceivable and will justify a further 

 test. 



"As to the life-and-death selection due to famine, it may be 

 said, in addition to the previous discussion of mortality among 

 the experimental silkworms, that while lots subjected to two years 

 of famine (themselves in one year, their parents in the year before) 

 were fertile in so far as number of young hatched is concerned, it 

 was found to be exceedingly difficult to rear from them a 1903 

 generation. Indeed, at the time of the second moulting there were 

 but nineteen individuals (and tolerably vigorous larvae they were) 

 alive in the lot which had experienced two years of famine, al- 

 though every individual of the 149 hatched was carefully preserved 

 and royally fed a fact which goes to prove that the equipment at 

 birth of many of these larvse was inadequate. 



"The fact that some larvae of starved ancestry have exhibited a 

 superiority over their fellows, in surviving and recovering from 

 hard conditions, is testimony for the existence of individual varia- 

 tions which cannot be defined anatomically, and yet which serve as 

 'handles' for natural selective agents. Such variations might be 

 called physiological variations, since it seems that the surviving 

 larvse must be those which are in best trim physiologically. These 

 larvae are able to make the most of the food offered to them. If 

 competition were allowed, they would probably be the individuals 

 which would cover the area most rapidly, securing whatever food 

 there might be. But under our experimental conditions there was 

 no competition allowed and yet certain precocious individuals made 

 more grams of flesh and more yards of silk, than other larvae 

 furnished with the same amount of raw material under like con- 

 ditions ; that this was due to the possession by the former of certain 

 congenital qualities of adaptability can scarcely be doubted. 



"As to the fertility of the variously fed lots, in so far as number 

 of eggs produced is a measure of fertility, our records already 

 demonstrate the fact that the better nourished are the more fertile. 

 Furthermore, the economy in this matter practised by the starve- 

 lings is not merely numerical, quality as well as quantity of eggs 

 being affected. In witness of this point may be recalled the story 

 of the dying 1903 generation, produced from eggs of the starvelings 

 of 1901 and 1902, which would seem to offer conclusive evidence 

 that a famine suffered by the parents works its way into the germ- 

 cells so that most of their progeny have but a poor birthright." 



