38 [I''cbniary, 



less deep depression, showing on the inside of the segment as a small 

 tubercle, and this may obviously be regarded as an excessively rudi- 

 mentary condition of the structure found in the female. 



Nut every species of Koptorthosoma, however, possesses the cham- 

 ber, for Dr. Willey has brought home from New Britain females of a 

 species, very closely allied to A", cestuans, which show no more trace 

 of it than do the males of those species above mentioned. In no true 

 XyJocopa (either ^ or ?),of which many species have been examined, 

 is there any chamber or orifice. The large Acarl 1 have not yet found 

 entirely outside the chamber. Minute examples often abound on the 

 thorax posteriorly, and sometimes may be seen arranged in a regular 

 transverse row at the base of the hairs. These may either be the 

 young of the large individuals, or belong to some other species. 



The fact that the chamber is found only in the female bees is of 

 interest and importance, for, as every Hymenopterist is aware, the 

 male bees are short-lived and vagrant, rarely returning to the nest for 

 more than a few days, so that parasites attached to this sex would be 

 placed under very disadvantageous circumstances. 



The hind portion of the thorax of Aculeate Hijmenoplera is always 

 a favourite resting place fur parasites, and it is probable that they 

 attack the soft membranes which connect the abdomen and thorax — 

 the only spot apparently that is open to attack. One may sometimes 

 pick up large Bomhl so weakened bj' these Acarid parasites as to be 

 quite unable to fly. Sharp has suggested [Ent. Mo. Mag., xv (1S7S), 

 p. 154] that the accurate co-adaptation of external parts of certain 

 beetles {Heliocopris) is for the purpose of excluding parasites from 

 parts liable to be attacked. We have seen a IStaphyliuid struggle 

 furiously to rid itself of a single minute Acarus. 



The protection afforded to the parasites by living enclosed is 

 obvious enough, and it would j)robably be an advantage to the bees to 

 have these large Acari confined in a special chamber. There is, how- 

 ever, no positive evidence that they do keep within it, and from the 

 fact that in dried specimens they are so often found partly emerging 

 from the orifice, the contrary would appear to be the case. 



Moreover, it may be observed in some species of the bees that a 

 row of stiff hairs is directed obliquely over the orifice from above, 

 as if to bar the way upwards, while on the lower side it is nearly or 

 altogether unprotected, and a deep groove extends directly from it to 

 the membranes of the abdominal articulation, as if to actually guide 

 the parasites to the weak parts. Around the point of articulation 



