392 LICE 



ber gradually rising, until after a week or so of egg-laying seven 

 to ten or more eggs may be laid eacK day. A day or two before 

 the end of egg-laying and the death of the louse the daily number 

 drops again. Eggs are laid whether copulation has occurred 

 or not, but in no case have unfertilized eggs ])een observed to 

 develop. One copulation is not sufficient to fertilize all the eggs, 

 but fertile eggs may be laid for at least 20 days after a single 

 copulation. According to Sikora, copulation normally takes 

 place at intervals of from one to three days. Egg-laying ceases 

 at temperatures below 77° F. and a daily exposure to a tempera- 

 ture of 60° F. for only two or three hours causes a marked falling 

 off in egg production. 



According to Sikora the eggs hatch in about six days at the 

 optimum temperature of 95° F. At a temperature of 77° F. 

 the incubation period is prolonged to 16 days, whereas at 68°, 

 lowered from 42° to 60° F. during the latter part of the night, or 

 at a constant temperature of 60° F., no hatching at all takes place. 

 At temperatures above 95°, also, the eggs suffer a high mortality 

 probably due to the difficulty in obtaining proper conditions 

 of humidity rather than to the direct effect of the heat itself. 

 Either excessive humidity or complete drying is fatal to the 

 eggs. It is evident that in winter the laying off of the clothing 

 at night in a cold room or the leaving of mattresses or bed clothes 

 in the daytime is sufficient to prevent the laying of eggs or the 

 hatching of eggs already laid, thus resulting in the extermination 

 of the lice. 



The newly hatched lice are almost perfect miniatures of the 

 adults, and are ready to feed almost as soon as they emerge from 

 the egg; in fact, they usually die in less than 24 hours if not 

 allowed to feed, though the adults can survive as much as five 

 days of starving. According to Sikora, the rapidity of the 

 development of lice is dependent on temperature and on amount 

 of food. At a temperature of 95° F. and with as many daily 

 feeds as would willingly be taken, namely six, the lice pass tlirough 

 their first moult in three days, the second in five or six days, and 

 the third, which ])rings them to maturity, in eight or nine days. 

 Reduction of daily feeds to two increased the period of develop- 

 ment to nine or ten days, whereas reduction of temperature to 

 75° F. by day and 95° F. by night, with two daily feeds, prolonged 

 the development to from 13 to 15 days. 



