CHAPTER VII. 



Order II. BDELLOIDA. 



Swimming ' with their ciliary wreath, and creeping like a leech; foot wholly retractile 

 within the body, telescopic, ending almost invariably in three tocs.^ 



The Leech-like Creepers form so natural a group of animals that all the classifiers of 

 the Eotifera have placed them by themselves. Ehrenberg, Dr. S. Bartsch, Herr 

 K. Eckstein, have arranged them in the family Philodincsa ; Dujardin, ui the order of 

 the Botiferes ; and Dr. Leydig, in his un-named second family of Eotifera " with a 

 long, jointed, telescopic, retractile foot." This extremely characteristic foot is to be 

 found only in the two families of this order, the PliilodinadcB and Adinctada. The 

 longitudinal muscles, which pass down the foot, end at intervals below each other, so 

 that their contraction draws the lowest part of the foot into that just above it, and this 

 in its turn is drawn mto the part above, and so on ; until the whole foot can be shut up 

 like a telescope, and withdrawn completely into the trunk. 



A special interest attaches to the BDELLOIDA. Specimens of various species in 

 both the families have been dried, suffered to lie m that condition for three or four years, 

 and then brought to active life again by being placed in water.^ I have no space to 

 give the history of this question, and of the controversies that have arisen about it, 

 some of which, indeed, are still as lively as ever ; I shall therefore confine myself simply 

 to a relation of facts whose reality may be easily tested, and of the satisfactory explana- 

 tion of them given by Mr. Davis."* If specimens of Philodina roseola be placed with a 

 little clear water on a slip of clean glass, and the water be quickly dried up, they will 

 all be killed ; no watering will revive them. I have tried this scores of times and never 

 met with a case of recovery. But if the rotifers be placed in a cell that contains a 

 little sand, or moss, then the ceU may be dried even in vacuo over sulphuric acid ; and 

 yet, when water is again added to it, in the majority of cases, some of the Eotifera wiU 

 be found to be still alive : or the cell with the water, sand &c., and the animals may be 

 gradually heated up to 200° Fahr., and yet some of the creatures will probably recover 

 if, when the cell is cool, fresh water be added : or once more, the cell may be laid aside 

 for several years in utter dustiness, and still, on the addition of a few drops of water, the 

 chances are that, in the course of an hour, a few of the animals will revive. Now the 

 real point is obviously this. If a Philodino can be revivified after having been dried in 



' [The swimming faculty in this order is very subordinate. We never see a Philodina or a Rotifer 

 sailing smoothly hither and thither, turning waywardly on its course, and roving about with no 

 apparent aim, like a Microcodon or a Eiiclilanis. It will bore through a mass of vegetation, and, on 

 coming to its margin, shoot straight away on a voyage of discovery. But the very first new bit of 

 sediment that it meets arrests it ; it instantly creeps into this, and makes this its home for a while : 

 as if its natatory powers were used merely for change of place, as distinguished from actual enjoyment 

 in swimming. — P.H.G.] 



^ All the known British species have three toes. Dr. L. K. Schmarda has described some foreign 

 species with only two toes ; but I think it probable that he is mistaken. 



^ Mr. Jabez Hogg {Eufjlish MccJianic, Jan. 16, 1885) says that he has seen rotifers revive " after 

 fifteen years' careful seclusion." 



' Mon. Micr. J. vol. ix. 1H73, p. 200. 



