EXPERIMENTS WITH PYEETHEUM. 21 



were lying helpless upon the table, although still retaining considerable 

 vitality. In twenty hours they were dead. 



EXPERIMENT NO. 7. — EXPERIMENT UPON LARWE OF DATANA MIX 



ISTRA. 



This experiment was conducted in the same manner as Experiment 

 No. 4. Three full-grown larva; of Datana ministra were placed in each 

 of nine tin boxes and sprinkled in the same manner with the same 

 amount of the different poisons. The boxes this time, instead of being 

 covered with their own tight tin covers, were covered with slabs of glass, 

 which, on account of the irregularities in the edges of the boxes, did not 

 fit tightly, and allowed for a pretty free circulation of air. But this per- 

 haps was compensated for by the fact that the covers did not have to be 

 lifted to observe the condition of the larvae. The fact should be remem- 

 bered in comparing this experiment with No. 4. The following table 

 shows the result, and it will be noticed that the Datana is susceptible 

 in a remarkable degree to the action of the pyrethrum when compared 

 with Hyphantria or Plusia : 



