22 
BULLETIN 1429, U. S. DEPARTMENT OF AGRICULTURE 
soil to the depth of 1 inch. Many of the larvae effected penetration 
within one or two hours after being placed on the grubs, but ordinarily 
the vials were set aside for 24 hours to insure a maximum parasitism. 
In 1922 porous-clay blocks were substituted for the vials, each of 
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•Reproductive organs of Prosena siberita: A,. condition before mating; B, after fertili- 
zation, showing eggs and larvae in the distended egg sac 
these blocks bearing upwards of 100 cells of a size suitable to accommo- 
date the grubs used. These blocks were more satisfactory in every 
way and resulted in a considerable saving in time. With this method 
it was possible for one person to inoculate more than 1,000 grubs 
per day, provided a sufficient number of flies were available. 
