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side to terminate in a somewhat slender point just 

 behind the insertions of the first pair of legs. An im- 

 portant character of this piece of the bee's outer skeleton 

 is the presence of a small rounded lobe which projects 

 backward from each side and overlaps one of the plates 

 belonging to the meso-thorax. 



Concealed beneath this lobe, and the space between it 

 and a side piece known as the episternal plate lies the 

 fateful stigmatic opening, through which Tarsonemus 

 woodi finds an entrance to the trachea of the bee. The 

 trachea probably belongs to the prothorax, although 

 its stigma lies in the soft chitin which joins the two 

 regions, pro- and meso-thorax. It is probably useless 

 to speculate as to whether the prothoracic tracheae 

 were first found by the invading mite accidentally or 

 whether the instinct to avoid light and enter crevices 

 charateristic of many such like creatures, directively 

 determined occupation of the bee. Anyhow, this par- 

 ticular stigmai is unusual in not being exposed as are 

 the others upon the body. These other stigmata all 

 pertain to the abdomen, and lead almost directly into 

 air sacs. The restricted capacity of the tracheae as 

 compared with that of the air sacs is evidently more 

 favourably to the mite, which although it has a free 

 passage from the tracheae to certain of these in the 

 thorax, yet never breeds in them. It is clear, at 

 all events, that however originated, the occupation 

 of the thoracic tracheae is not now a casual one, 

 since these thoracic tracheae are the only breeding 

 place of this species. Tarsonemus woodi is unquestion- 

 ably a true endo-parasite, and I believe this is the only 

 case of the kind known amongst acarines, although it is 

 more than probable that future investigation will 

 reveal other instances of a similar nature. 



The stigmata leading to the tracheae are each pro- 

 vided with a blocking plate, by means of which the bee 

 can at least partially close the tubes. Under what 

 circumstances this function is exercised has not been 

 determined, but as great difficulty has been experienced 

 in endeavours to kill mites within the respiratory 

 system by means of acaricides, it would appear as if 

 where substances are offensive or irritant, the bees en- 

 deavour by closure to keep them out. 



