36 LIFE HISTORY OF NORTH AMERICAN TICKS. 
tures. In reckoning the effective temperature where the daily 
mean does not fall below 43° F. the average daily mean for the period 
covered may first be obtained; then, by subtracting 43° F. (the 
“‘zero”’ of effective temperature) from this mean and multiplying 
the product by the number of days covered, the total effective tem- 
perature can be readily calculated. Since the monthly mean tem- 
perature must first be obtained, by following this method much time 
may be saved in calculating the total effective temperature. Where 
the mean temperature for one or more days during a given period 
falls below the ‘‘zero”’ of effective temperature (43° F.), the effective 
temperature for cach day should be obtained and added in computing 
the tetal effective temperature. Our records on the incubation of eggs 
are based largely upon lots kept in glass tubes on sand. 
RECKONING PERIODS. 
In determining periods it has been the practice to commence with 
the day following dropping or hatching of the tick and to include 
the day oviposition commenced, molting occurred, or death took 
place, as the case might be. In calculating the period of incubation 
the day of oviposition as well as the day of hatching has been included, 
as in the case of the determination of effective temperatures. 
In the life-history work in the laboratory it was the daily practice 
between the hours of 3 and 5 p. m. to separate the eggs from the 
females,! the molted ticks from those not molted, and to note the 
hatching of eggs. In case more eggs had been deposited than could 
be counted within this period, they were isolated in pill boxes and 
counted the following day. After the eggs were counted they were 
placed on sand in tubes. Thus the records of egg counts, moltings, 
and other life changes, as recorded in the tables here given, are for 
periods of about 24 hours. 
In determining the periods of attachment, when these records have 
been made by the utilization of the bovine scrotum, it has been the 
practice to place the larve, nymphs, or adults in a cotton bag secured 
to the host. The bag was examined at periods of 10 to 12 hours 
and attachment noted. ‘Ticks still in the bag at the end of 24 hours 
were usually removed. In some cases, however, ticks have been 
kept in the bag for longer periods, but attention is called to these 
cases where they occur. Some ticks have been found to remain upon 
the host for several days unattached or without attaching securely. 
This might or might not occur naturally, but must be taken mto con- 
sideration. Where small mammals were employed for the engorge- 
ment of ticks, in most cases the individuals were examined at frequent 
intervals, so that the time of attachment was noted rather accurately. 
1JIn determining the number of eggs deposited by a species only females that have been permitted to 
drop should be used. 
