276 Remarks on Paper " On the Desiccation of Rotifers." 



great majority die only too easily, and decay rapidly. Very few 

 Eotifers will bear even a momentary withdrawal of the water in 

 which they swim, and all the species that I am acquainted with can 

 be easily smothered by being kept in a small air-tight cell. Un- 

 fortunately the student can obtain but little advantage from so 

 killing them, as they usually begin to disintegrate the instant they 

 die ; the trochal disk, for instance, disappearing as it ceases to move. 

 The case is no better if they die naturally. I have seen, for 

 instance, a Triarthra suddenly roll down dead to the bottom of a 

 live cell, and decay so quickly that the outline of its muscles had 

 become indistinct before I could change a low power for a high one. 



The notion that any sort of treatment and any dirty water will 

 do for Eotifers is a very erroneous one. It is true that Rotifers 

 are to be found in very dirty ponds ; but every species has its own 

 habitat, and it would be as useless to look for Brachionus annularis 

 in a clear pool, as for a Euchlanis in a farmer's duck-pond. 



A slight alteration in the conditions of life is fatal to most of 

 them ; and, so far as my experience goes, it is impossible to preserve 

 the finer species in tanks at home for more than a few days. A 

 student of Eotifers must therefore be one who knows all the ponds 

 for miles round his own house, and who is constantly out looking 

 for fresh specimens ; and he will find that neither air-pumps, nor 

 sulphuric acid, nor hot ovens are wanted to kill off his live stock, 

 but that they will die of their own accord with the most provoking 

 regularity. 



I have been tempted by my subject into a rather long digression ; 

 but I cannot conclude my paper without reverting to Mr. Davis' 

 happy suggestion, that the Philodines protect themselves against 

 the effects of drought by secreting a viscid envelope during the 

 slow evaporation of water entangled among particles of sand. Most 

 of the Eotifers possess, in some degree, the power of secreting such 

 a fluid. Some (as Rydatina, Synchseta, Rhinops, and Pedalion) 

 use it to enable them to adhere to external bodies, others (as 

 Melicerta, Limnias, CEcistes) to form an inner tube, round which 

 their outer cases are built. Mr. Davis now tells us that some of 

 the Philodines put this secretion to a hitherto unsuspected use, and 

 that they coat themselves all over with it so as to resist a drying 

 that would otherwise be fatal to them. This solution of a much- 

 vexed question is as ingenious as it is probable and new; and 

 although it may possibly require confirmation from future observers 

 and experimenters, I have little doubt that such confirmation it will 

 receive. 



