744 



SCIENCE. 



[N. S. Vol. XVIII. No. 467. 



that lettiice-made silk is worth the cost of 

 double labor. 



The other variations noted among the 

 lettuce-fed 'worms' have to do with the 

 larva and cocoon. All of the lettuce-fed 

 larvffi appeared to be unusually 'thin skin- 

 ned,' the body wall being stretched and 

 shiny. The larvte were at all stages char- 

 acteristically heavier than mulberry-fed 

 larvae, each of them weighing at spinning 

 time as much as, and two of them weighing 

 400 mg. more than the heaviest of the mul- 

 berry-fed. The weights of the cocooned 

 pupffi were somewhat above the average 

 among the mulberry-fed, a fact due to the 

 large piipa rather than to the amount of 

 silk in the cocoon, as was demonstrated by 

 weighing cocoon and pupa separately, 

 whereupon it was found that the cocoon 

 was, on the average, but one half as heavy 

 as that of the average among the mulberry- 

 fed, in some cases falling as low as two 

 fifths of the mulberry cocoon's average 

 weight, and in no case rising above three 

 fifths. The silk appears to be less strong 

 and elastic than that of the mulberry-made 

 cocoon. 



2. In the mulberry-fed worms there ex- 

 ists a very definite and constant relation 

 between amount of food and size as indi- 

 cated by weight, the starveling individuals 

 being consistently smaller than the well- 

 nourished, the lingering effects of this 

 dwarfing being handed down even unto the 

 third generation, although the progeny of 

 the famine generation be fed the optimum 

 amount of food; in case the diminished 

 nourishment is imposed upon three or even 

 two successive generations there is pro- 

 duced a diminutive, but still fertile, race 

 of Lilliputian silkworms whose moths, as 

 regards wing expanse, might join the ranks 

 of the micro-Lepidoptera almost unre- 

 marked. 



In illustration may be quoted the typical 

 or modal larval weights for each of the 



lots of 1903 at the time of readiness to spin, 

 which marks the completion of the feeding 

 and is, therefore, an advantageous point 

 for a summary of the results of the three 

 years' experimental feeding. 



The history of the eight lots referred to 

 may be gathered from an examination of 

 the accompanying table, in which ' ' means 

 optimum amount of food and 'S' means 

 short rations. The column to the right 

 indicates the relative rank of the various 

 lots as judged by the modes of frequency 

 polygons erected to include all the indi- 

 vidual weights for each lot at spinning 

 time. 



We find that control lot 1, consisting 

 of normally fed individuals of normal 

 ancestry, holds first rank in weight, as 

 was to be expected. Second comes lot 5, 

 whose grandparents experienced a famine 

 but whose parents as well as themselves 

 enjoyed years of plenty. Lots 2 and 3 

 have likewise had one ancestral generation 

 on short rations, and the fact that they 

 are lighter in weight than lot 5 illustrates 

 a general rule which obtains throughout 

 the entire company of experimental worms, 

 namely, that the effects of famine grow 

 less evident the further removed the indi- 

 viduals are from its occurrence in their 

 ancestral history. Thus lot 5 is two gen- 

 erations removed from the famine of 1901, 

 while lot 3 has had but one generation in 

 which to recover its ancestral loss. Lot 2, 

 which has had a total of but one famine 

 year — the current year— nevertheless ranks 



