54 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 1 



cases, the results would be more exact because computations would 

 begin on the exact date cattle were placed in the pastures, while 

 those made in the office of the entomologist would necessarily be more 

 or less generalized. The only apparatus necessary for the ranchman 

 would be a set of maximum and minimum thermometers and the only 

 work involved, the keeping of the record of the average daily mean 

 temperature and the accumulated effective temperature from the date 

 the cattle were placed on the tick free area. 



Possible Criticisms. — The criticism might be made that studies re- 

 ferred to in the foregoing do not take into consideration factors other 

 than temperature which might influence incubation. Among these 

 might be mentioned: (1) moisture; and (2) accidental heat, as for 

 instance from manure piles. Regarding moisture, it may be said 

 that tick eggs are susceptible. A certain degree of dessication abso- 

 lutely prevents hatching. Nevertheless our data have been drawn 

 from eggs placed under a variety of conditions and due allowance 

 has been made in the law for the usual seasonal variations. Our 

 figures are not from individual lots of eggs, but averages from many 

 lots under different conditions. The accidental heat from manure 

 referred to at most could be but an exceedingly unimportant matter. 

 About barns it might be worthy of consideration, but in pastures for 

 all practical purposes it would be absolutely negligible. 



There is a margin for possible error in the temperatures that may 

 occur between the time a prediction is made and the actual time of 

 hatching. Unusual variations may lengthen or shorten this interval. 

 This obviously will always make it impossible to predict the exact 

 time of hatching. Nevertheless, close approximations can be made 

 and these will serve every practical purpose. The entomologist can 

 always take pains to be on the safe side by allowing for the highest 

 temperatures known for the period between the date of the prediction 

 and the forecasted date of hatching. 



In conclusion, it seems that the present proposed law is at least as 

 tangible as any temperature law proposed with reference to insects. 

 Strictly tentative as it is and subject to possible important modifica- 

 tions or even absolute nullification as the result of further data, at 

 this time it seems to have practical possibilities. Though not as im- 

 portant as Doctor HoAvard's rule regarding the yellow fever mos- 

 quito, it is at least as definite, for the factors that could possibly 

 vitiate it are no more important than in that case. On the other 

 hand the law cannot be as exact as Wallich's rule governing the 

 hatching of fish eggs, because in that case all the varying influences 

 of the air are absent and replaced by less important ones in the water. 



The law dealt with in this paper was given preliminary notice in 



