78 INHERITANCE IN SILKWORMS^ I 



eating to begin spinning, through periods of two days before, three days before, 

 four, five and so on to twelve days before, the twelve-day period being the whole 

 of the feeding period normally lasting from the fourth moulting up to spinning 

 time. 



From these results it may be said that silkworms may be cut off from a food 

 supply nearly seven days before the normal limit of their feeding time and yet 

 complete their development (spin, pupate and emerge as imago). These seven 

 days represent a little more than half of the last intermoulting actively feeding 

 period, or about one-ninth of the whole larval (feeding) life. The deprivation 

 of food for from one to four days seems neither to hasten the metamorphosis 

 nor to modify it appreciably, nor to result in the production of a moth of lessened 

 size or lessened fertility. The larvse deprived of food not more than four days 

 before normal close of feeding time do not immediately spin and pupate, but 

 wait restlessly for the normal time of pupation (approximately twelve days 

 after the fourth moulting), and then normally spin and pupate. If deprived of 

 food for more than four days and less than seven, the larvae shorten their last 

 intermoulting stage to about seven days, forming, however, a normal cocoon 

 and transforming into a normal moth. If the larvae are deprived of food eight 

 days or more before their normal spinning-up time, they invariably die without 

 forming a cocoon, and in only one case was pupation accomplished. A begin- 

 ning at spinning is made by larvae fed for more than two days after the fourth 

 moulting, but no spinning at all is done by larvae deprived of food from the day 

 of fourth moulting or from the first or second day thereafter. 



The twentieth larva of the lot was to be deprived of food 216 hours after 

 the fourth moult, but it began spinning up in 200 hours (eight days) after, and 

 pupated on the following day. Here is a normal variation of four days out of 

 the usual twelve of the last feeding stage, just about as much shortening as the 

 extreme that could be induced by actual deprivation of food. 



Loss of Weight During Pupal Life. — A belief among commercial breeders 

 of silkworms that there is a loss in weight of the cocoons (silk) accompanying 

 pupal life is indicated by their recognized wish to make an early sale of the 

 cocoon product. This loss is generally attributed to "evaporation from the 

 cocoon." The question arose as to whether the loss in weight of the pupa- 

 containing cocoon might be not a loss in weight of silk but an accompaniment 

 of developmental changes in the pupa, a process in which stores of nourishment 

 (in the larval body) are being converted into moth with chemical changes which 

 might occasion some loss in weight. Therefore in four individuals the cocoon 

 and pupa were weighed separately once each day from the time of pupation to 

 time of emergence of the moth, while at the same time the daily weights of the 

 naked chrysalids of three other lepidopterous species were determined to see 

 if a loss of weight accompanied pupal aging in them as well as in the silkworm 

 moth. From the data obtained it is apparent that the silken cocoon loses a very 

 small amount, about 4 per cent., of its weight in the first day after its completion, 

 and then loses no further weight; that the pupa loses weight slightly but per- 

 sistently and steadily from day to day throughout its entire duration, the total 

 loss amounting to about 14 per cent. ; and that the pupa; of three other lepidop- 

 terous insects, namely, the tent caterpillar {Clisiocampa sp.), checkerspot butter- 



