44 OYSTER-SHELL BAEK-LOIJSE. 



the case is none the less interesting, as showing that parasitic in- 

 sects, even of the most minute character, can be transported, in 

 sooie instances, with perfect ease and certainty, and should cau- 

 tion us against dismissing the whole subject from our minds, as 

 we have been inclined to do, as impracticable and absurd. 



POSTSOKIPT. 



Since writing the above, my friend Capt. Edward H. Beebe, of 

 Galena, procured and transmitted to me (Nov. 8) a number of 

 apple twigs, obtained partly in that town and partly from the 

 Southern part of Wisconsin, a section which has suffered more 

 from the depredations of the Bark-louee than almost any other 

 locality. A very brief inspection of these twigs was sufficient to 

 show that onr infinitessimal friend, the Chalcis, has not yet found 

 its way to that region, or at least not to that particular locality. 

 Not a trace of it could be discovered, either by the round holes in 

 the scales or the presence of the larvss beneath them. The dis- 

 appointment, however, was somewhat mitigated by finding that 

 more than two-thirds of the scales are, nevertheless, from some 

 cause or other, aburiive. Upon carefully raising and examining 

 two hundred scales upon six different twigs, sixty of them were 

 found to contain sound eggs of the Bark-louse, and one hundred 

 and forty were abortive. These abortive scales present the same 

 appearances that such scales have when obtained from other lo- 

 calities ; that is, a small proportion of them contain only the thin 

 and dried remains of the female Bark-louse, who has perished 

 from some cause, without depositing or perhaps even forming her 

 eggs. But most of the scales exhibited the brownish, granulated 

 mass which they generally contain, and which we may presume 

 to consibt of shrunken and discolored eggs. This mass of debris 

 also has, in most cases, a furry aspect, which is probably owing 

 to mould. 



The interesting question here arises, what, in the absence of 

 the Chalcides, has caused the destruction of this large proportion 

 of the bark-lice and their eggs ? I searched carefully for Acari^ 

 and lest, from their minute size, I might overlook them with a 

 common lens, I put many of the scales under the microscope, but 

 did not detect more than half a dozen in all; just enough, how- 

 ever, to show that they are not altogether absent. All the phe- 



