Dkckmbek n, 1!)03.] 



SCIENCE. 



7-47 



time (emphasized eougenital differences 

 again), with a safer criterion, as to their 

 relative proiiiptness, in the column between 

 the extremes— a column of tigures int<.>nded 

 to show the relative i)romptness with which 

 a two thirds majority of the larva? in each 

 lot arrives at the spinning time, this pro- 

 portion being taken to represent the typical 

 condition for the lot. The order in which 

 the lots are arranged in this cohimn cor- 

 responds in a general way with that preva- 

 lent 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. hut 

 does not lend support to the notion of 

 natural selection on a food scarcity basis, 

 as previon.sly suggested. Lot 8, which has 

 had no relief from famine during the en- 

 tire three years, brings up the rear at the 

 spinning, as might be expected. 



This check upon functional activity ex- 

 ercised by diminished nourishment affects 

 the moulting, the time for the connnence- 

 nient of spinning and the issuing time for 

 the adults, but the time spent in the spin- 

 ning of the cocoon, from its beginnings in 

 the threads of the supporting net to its 

 apparent completion when the cocoon be- 

 comes opa<|Ue, is practically identical for 

 under-fed and well-fed individuals. A 

 rea.son for this exception to the tardy 

 habits of the under-fed is to be found in 

 the fact that the under-fed lai'va- pi'iidnce 



less silk (less in size, thickness and weight) 

 than the well-fed, thus accomplishing more 

 meager results in the same amount of time. 

 That the individuals sentenced to short 

 rations should produce less silk than their 

 well-fed neighbors is certainly to be ex- 

 pected, silk not being made without leaves 

 any more readily than bricks without straw. 



4. Not only do short rations protract the 

 time appointed for the spinning, moulting, 

 etc., but they appear to have a more strik- 

 ing effect upon the actual occurrence of the 

 moulting. The normal number of moults 

 for the silkworm larva is four. Five 

 moults have occurred for most of the indi- 

 viduals belonging to the under-fed lots of 

 19Q2 and 1903, whereas none of the well- 

 fed individvials has undergone a fifth 

 moult. It would seem, therefore, that the 

 occurrence of a fifth moult may be fairly 

 ascribed to a reduction of food ; at least a 

 fifth monlt very frequently accompanies it 

 and has suggested the possibility that the 

 enforced fasting of the under-fed larva— 

 in the intervals between meals— may have 

 the same phy.siological effect as the normal 

 fasting which precedes the normal moult- 

 ing, during which time the so-called 'moult- 

 ing fluid' is secreted. That this effect may 

 accumulate throughout the lifetime of the 

 larva until the lai'va 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. 



5. 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 sub- 

 jected to two years of famine (themselves 

 in one year, their parents in the year be- 

 fore) were fertile in so far as number of 

 .voung hatched is concerned, it was found 

 til be exceedingly difficult to rear from 

 them a 1903 generation. Indeed, at the 

 time of the second moultini; there were but 



