OYSTER-SHELL BARK-LOTJSE. 33 



curately determined. Upon raising many of the scales in the fall 

 of the year, we find them destitute of the eggs of the bark louse 

 which should naturally fill them at this season. In their place we 

 find a confused and discolored mass which we suppose to be the 

 remains of the legitimate occupants, that is, the eggshells and the 

 dried up body of the mother louse. 



Amongst this debris the minute Acari are sometimes seen, and 

 to them the ruin is generally attributed. But in most instances, 

 so far as 1 have observed, no Acari are found, and some scales are 

 almost wholly empty, so that if the Acari caused the destruction 

 in both cases, they must, in the former instance, have done their 

 work and left, and in the latter they must have devoured the 

 mother louse, Qg^ shtjlls and all. But it is of no consequence to 

 us who or what has wrought the ruin, so long as the bark-lice are 

 destroyed. The important question is, what proportion of the 

 bark-lice are destroyed, by any and all causes, and what part 

 remain to propagate the race for another year % 



Mr. "Walsh, after examining many hundreds of scales in the 

 summer of 1867, stated that the largest proportion which he had 

 ever found with their contents destroyed, ^as two-thirds. From 

 this form of expression we infer that it was only in certain cases, 

 or perhaps localities, that so large a propqrtion were abortive, and 

 this destruction he attributed solely to Acari. 



The following observations will exhibit the matter in a more 

 definite light. 



On or about the twentieth of September, I examined all the 

 scales on four twigs, taken from different trees, and from two 

 gardens remote from each other, with the following result : 



Whole number of scales ^ . 330 



Number of scales with round holes, through which the Chalcides had escaped 116 



Number of scales having under them the larvse of the Chalcides 95 



Number of scales, the contents of which have been destroyed by Acari, or unknown 



causes • 85 



Scales with ragged holes eaten by Coccinellffi 7 



Scales containing more or less sound eggs 27 



Whole number 330 



Oct. 20th, examined four twigs taken from different trees : 



Whole number of scales 284 



— a5 "^ 



