" On the Desiccation of Rotifers.'" 275 



pletely desiccated" and yet recover, and others that they do not 

 recover when " a certain degree of desiccation has been exceeded." 



The latter statement is, of course, a very safe one ; but, cautious 

 as it is, it does not in the least meet the real difficulty of the case, 

 which is briefly this, viz. that every Eotifer, when isolated and laid 

 with a drop of clean water on a slip of clean glass, dies if the water 

 be allowed to evaporate. Now, if a Eotifer will bear drying in an 

 air-pump with sulphuric acid, or in an oven, why will it not bear 

 simple evaporation on a slip of glass ? No one will maintain that 

 one's sitting-room is drier than the inside of an oven at 200° Fahr. 

 or of a receiver ; and if dryness kills the animals on the glass, why 

 does not the greater dryness of the air-pump, or oven, kill them ? 

 Doubtless Rotifers can be killed by heated air; that might have 

 been taken for granted ; but, if they survive such heat and drying 

 as have been detailed above, why cannot they recover from the 

 effects of evaporation in the comparatively moist air of a sitting- 

 room ? 



It has been suggested that particles of sand or dirt saved the 

 Eotifers in the air-pump ; and that the animals died when isolated 

 on a glass slip from not being able to bury themselves under 

 protecting rubbish. But this explanation will not meet the case of 

 the Eotifers that survived a heat of 212° Fahr. It is of course 

 easy to conceive that an animal which lives in water may lie 

 dormant out of it, provided its own internal fluids are not dried up ; 

 but how can sand as hot as boiling water help to protect from 

 evaporation the internal fluids of a soft- bodied Philodine ? 



Once more I state what appears to me to be the real point at 

 issue. Why will not Eotifers when freed from extraneous particles 

 bear drying in the open air, and yet survive when surrounded with 

 such particles after drying in a vacuum or an oven ? This is the 

 riddle; and of this riddle no one, I believe, but Mr. Davis has 

 attempted the solution. Mr. Davis states that it is by secreting a 

 gelatinous coat that the Eotifer in the air-pump resists a desiccation 

 which would be otherwise fatal to it. The question at once arises, 

 " Why does not the Rotifer do the same when freed from the sand ? " 

 Mr. Davis' answer on this point is equally complete; the evapo- 

 ration on the clean glass slip is too rapid to permit of the necessary 

 secretion, and the animal also is too restless under the unpleasant 

 circumstances in which it finds itself to attempt to form the 

 protecting coat, even if it had the time for doing so. I have dried 

 hundreds of Philodines on glass, and have watched their actions 

 while the water evaporated, and I can fully corroborate Mr. Davis' 

 assertion. I can add also that not one of those many hundreds 

 ever came to life again. 



It might be imagined from such discussions as the above that 

 Eotifers are as a class very tenacious of life ; but the fact is that the 



VOL. IX. X 



