COLLECTION OF BDELLOID AND OTHER ROTIFERA. 221 



proof investment. Under natural conditions there is of course 

 plenty of sand or vegetable fibres. 



Once safely covered with his " airproof," the rotifer can 

 endure months of desiccation, and in some cases they have been 

 revived after several years. But the longer the period of 

 desiccation, the smaller will be the proportion of the individuals 

 that revive. In other words, the best results are obtainable 

 from dry mosses when they are freshly gathered or, at least, 

 not more than three or four months old. 



When " wet " mosses are washed, the rotifers are active at 

 once when the moss is placed in water ; they have, in fact, 

 never ceased their active life. They may have contracted 

 themselves and may be lying motionless, but that is because 

 they have been disturbed, and are temporarily frightened or 

 simply timid and cautious. When " dry " moss is washed, 

 some time must be allowed for the water to dissolve the protec- 

 tive coating, and to stimulate the dormant life to a renewal of 

 activity. The time varies according to the period which has 

 elapsed since the moss was collected. In the case of mosses 

 recently gathered, it may be as short as ten minutes ; in that 

 of mosses which have been in hand for many months, it may 

 be several hours before the animals begin to show signs of re- 

 turning animation. Whatever be the period, part of it can be 

 usefully employed in " clearing " the water of the " stock." 



Mosses from wet banks and all dry mosses should be gathered 

 with as little earthy matter about their roots as can be managed 

 without dislodging animals adherent to the stems and leaves. 

 With short-stemmed mosses some thickness of earthy material 

 is unavoidable. Before washing such material, I generally shave 

 or scrape off the moss-fibres just above the surface of the soil, 

 to avoid putting the latter in the water. Even then a consider- 

 able proportion of dirt particles in the stock must always be 

 expected in washing dry mosses. Most of it is usually sand, 

 which will settle quickly when the stock is stirred or shaken up, 

 and is not harmful. But there is always a proportion of very 

 finely divided particles which remain suspended in the water after 

 the sand has settled. These finer particles doubtless include 

 great numbers of bacteria and much decaying organic matter. 



JouRN. Q. M. C, Series II.— No. 80. 17 



