9G THE EOTIFERA. 



sand over sulphuric acid, or gradually heated to 200° Fahr., or left to the neglected dust 

 of years, why will it not recover from the effects of quick evaporation, without sand, on 

 a glass slip, in the comparatively moist air of a sitting-room ? It has been suggested 

 that, by burying itself in the sand, the animal obtains a covering to protect its internal 

 fluids. But this explanation does not meet the case of Rotifera heated in sand up to 

 200" Fahr. Surely hot sand at this temperature would be a poor protection for the 

 natural juices of a soft-bodied Rotiferon. On taking some earth or sand containing 

 dried-up Philodines, we shall see them dotted here and there, adhering to the earth's 

 particles, and looking like little red, orange, or white balls. If one of them be picked 

 out, and a drop of water placed on it, after a quarter of an bom - or so, a part of the 

 infolded foot will usually shoot out with a jerk, and the foot itself will then gradually 

 lengthen joint by joint. Often, at this stage, the jaws will be seen to be at work, and 

 the head will be driven out with its corona and wreaths still furled : at last these in 

 their turn open, and the recovered animal begins to roam about, or to work for food. 

 Now if, before we moisten the rotiferous earth, a bright light be thrown down on the 

 ball-like Rotifera, it will be seen that each globe has a nearly smooth glittering surface, 

 as if it were coated with a gelatine that filled up the hollows between the stout ridges 

 which run from head to foot. This is the key to the puzzle ; for Mr. Davis suggests 

 that the rhilodine survives the air pump, oven, and sun-baked gutter, by drawing-in its 

 head and foot into a ball, and then secreting round itself a gelatinous coating which 

 hardens in air and effectually preserves its internal fluids from evaporation. That the 

 gelatinous coat does preserve these fluids Mr. Davis proved by crushing the little balls 

 and finding them all moist within. 



But why can the creature do this when sand or moss is present, but fail to do it 

 under much less severe trials in their absence ? Here, too, Mr. Davis's explanation is 

 complete. The water dries more slowly when there is sand or moss in it. 1 The Philo- 

 dines (who are gutter-lovers) are trained in being dried up under these conditions. 

 They naturally creep to the little heaps of sand &c, where the water lingers longest, 

 and, finding it going, contract themselves into a ball, pour out a viscid secretion over 

 their bodies, and prepare for the worst. But all this takes time, and, on the clean glass 

 slip, not only does the water evaporate too quickly, but the animal is too restless in the 

 unusual conditions in which it finds itself to attempt its ordinary defence. As I have 

 often seen, they roam about, vainly seeking shelter, till it is too late ; they are overtaken 

 by the rapidity of the evaporation, and dry up never to recover. 



' It has been questioned whether the presence of sand in a cell, or in a gutter, does retard the 

 evaporation of the water. An experiment or two would soon satisfy a doubter ; and a little considera- 

 tion will show the cause of the retardation. When a drop of water is enclosed by three or four morsels 

 of silex, nearly in contact, it is protected by the silex from evaporation everywhere except at the 

 surface. In fact it is in a similar condition to water in an uncorked bottle. Of course the water will 

 dry up in such a bottle at last, but it will evaporate very much more slowly than it would do were it 

 poured out on a marble slab. 



If Philodines be left in a zoophyte trough, they will often be found dried up in one of its corners, 

 for the water lingers longest in the angle formed by the bottom and sides. Their instinct leads them 

 too, when other defences fail, to gather together in clusters so as to protect the evaporating water by 

 their own nearly-touching bodies. The Rev. E. J. Holloway, taking advantage of this habit, has suc- 

 ceeded in drying up groups of P. roseola, on slips of clean paper, quite free from sand or rubbish 

 of any kind. He kindly sent me two or three of these slips ; and an inspection of them under the 

 microscope confirmed the correctness of Mr. Davis's theory. The fibres of the paper had evi- 

 dently delayed the evaporation long enough to enable the rotifers to resort to their customary 

 defence. Each Philodine is the centre of a patch of glutinous secretion, which meets the similar 

 patches, surrounding its neighbours, in a succession of straight lines ; so that the whole group has 

 quite a tesselated appearance. Here and there, where fibres pass over or through a group, long tongues 

 of the secretion stretch from the animals to the fibres ; and, in one case, a rotifer, that had tried to 

 squeeze itself under some interlacing fibres, had been caught ; and, so held, had been moored to half-a- 

 dozen others by radiating viscous cords. The efficiency of the protection was at once shown by dipping 

 one of the slips into water, and watching the Philodines revive as the secretion dissolved. 



