OR^LIFE-HISTOET OP CERTAHS" ACAEINA. 381 



The hot-bed for cucumbers at the same place, whicli was made 

 up from the stable-manure, and which presented equally favour- 

 able conditions, swarmed with Sypopi, whicb covered every 

 small dipterous insect that emerged from the hot-bed. 



I now endeavoured again to try the converse experiment. I 

 collected a number of Tyroglyphi and placed them in two kinds 

 of glass cells, viz.: — 1, the small cells which I use for breeding Ori- 

 batidse, which are covered up by a glass plate, and in each of which 

 I only put one or two specimens, so that I can watch and know 

 each individual ; 2, the other, the larger cells (small dissecting 

 troughs), which I use for breeding Gamasidge, where the cover 

 is pierced with a few small holes, with muslin over them, so 

 placed that they can be made to communicate with the interior 

 of the cell or not as desired, by moving the cover : in these cells 

 a number of specimens can be placed if it be wished. I now 

 tried similar cells, each with a number of Tyroglyphidse, and, when 

 they were breeding freely, allowed one cell to get dry and kept 

 the other in proper hygrometric condition. I did not find that 

 I got more Hypopi in the cell that dried than the other; on the 

 contrary, I got more Hypopi where breeding was under favour- 

 able circumstances, and, consequently young nymphs more abun- 

 dant; but I did find that as the cell dried the Tyroglyphidse 

 retired into any hole or shelter which afforded a prospect of re- 

 taining moisture. Thus I kept a small piece of blotting-paper in 

 the cell in order to damp when more moisture was required, for 

 actual water must not be put in in drops on the glass, or the 

 Acari will drown. As the cell dried, I sometimes found that the 

 Tyroglyplii all got under the blotting-paper, and I could not see 

 one of them ; but if the drying process were stopped short of 

 what would destroy life, and fresh moisture added, they soon 

 came out again ; if fresh moisture were not added they died, and 

 were not seen again. The Hypopi endured drought better, but 

 if it were continued, they died also. I repeated these experi- 

 ments several times, but always with the same result. This may 

 possibly account for the way in which Megnin's Tyroglyplii dis- 

 appeared and Hypopi appeared when the cell got dry, and the 

 former reappeared on adding fresh fungus, in his glass cages con- 

 taining strips of fungus. However that may be, I did not suc- 

 ceed in producing or hastening the change to Hypopus by drying, 

 either in the larger cells, or in the smaller where I could watch 

 the individual Acarus. 



29* 



