82 



INHERITANCE IN SILKWORMS^ I 



This period in the silkworm's life is particularly advantageous for 

 consideration here because it marks the completion of the feeding, so that the 

 individuals of under-fed ancestry have been given the best chance to recover, 

 while those subject to altered food conditions have had the benefit of the altera- 

 tion during the entire food-taking period of life. 



In the table "O" means optimum amount of food and "S" means short rations. 

 To the right of the history of the lots is a section showing the rank of the lots 

 as to the extreme time limits of the spinning time (emphasized congential 

 differences again), with a safer criterion, as to their relative promptness, in the 

 column between the extremes — a column of figures intended to show the relative 

 promptness with which a two-thirds majority of the larvae in each lot arrives 

 at the spinning time, this proportion being taken to represent the typical condi- 

 tion for the lot. The order in which the lots are arranged in this column 

 corresponds in a general way with that prevalent for the weights at spinning 

 time, and the generalizations indulged in there may with few exceptions be 

 applied here. The lots which were well fed during the 1903 generation are ahead 

 of all of those given short rations in 1903, whatever ancestry they may have had. 

 Lot 1 leads here as in the matter of weight. Lots 3 and 5 tie for second place, 

 having held second and third places in weight. Lots 2 and 4 stand in the same 

 relation to one another that they held as to weight. Contrary to the weight 

 relation, lot 6 follows lot 2 at the spinning — a fact which illustrates again the 

 general rule that two generations of famine are more disastrous than one, but 

 does not lend support to the notion of natural selection on a food scarcity basis 

 as previously suggested. Lot 8, which has had no relief from famine during the 

 entire three years, brings up the rear at the spinning, as might be expected. 



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 



