136 B1UT1SH TYKOttLYPHIM. 



creature. The cover should be removed, first making 

 sure that the Acarus is not on the under- side of it, 

 every day, or at least every second day, and the cell 

 placed on the stage of the microscope and carefully 

 examined. 



I find it best and most reliable to have only one 

 Acarus in a cell ; for observation there should never be 

 more than three, and if there be more than one all but 

 the one to be most carefully observed should be taken 

 out at any time when there is any possibility of con- 

 fusion between them ; this I invariably did. I am sure 

 that in order to trace the life-histories the observer 

 should know each individual Acarus which he is 

 rearing ; this greatly increases the difficulties, because 

 it is easy enough to rear them in numbers in large 

 vessels with plenty of unsterilised food ; but far more 

 difficult to do so in such a manner as to be certain that 

 one's observations in each case are invariably of the 

 same individual. 



I had a number of these cells, always full, throughout 

 my experiments ; during what are called below the 

 winter experiments I had 29 cells; during the summer 

 observations 19. Whenever the Acarus or Acari in 

 one cell died, or otherwise became useless, it or they 

 were replaced by another or others, a fresh series in 

 that cell being started ; these series were numbered. 



The species which I tried to observe were Tyro- 

 ghjpJms siro, Carpoglyphns anonymus, and Hist log aster 

 entomophagus. I found the last-named species far the 

 best for my purpose, and the whole of the observations 

 which I have recorded in this connection were made 

 on this species. I found that the habitat of C. anony- 

 mus was not very suitable for such close observations 

 as I wished to make (it wades on wet preserved 

 fruits, etc.). T. siro is an active species, very apt to 

 escape when the cover is removed for examination of 

 the cell. H. entomophagus is a slow creature, which 

 did not escape readily; I had an ample supply of 

 the species upon ergot of rye, obtained for me by the 



