400 



ROTIFERA. 



Ehrenberg on the subject of animalcules are en- 

 titled to great respect, we think that he has not 

 investigated this subject with the candour that 

 would entitle his conclusions to confidence. 

 There is no a priori evidence why a perfect 

 desiccation and suspension of the functions of 

 life should not take place. This is the natu- 

 ral condition of the embryo of the seeds of 

 many plants, which, after hundreds of years, 

 when placed in proper circumstances, will 

 exhibit all the functions of vegetable life. 

 Amongst the highest forms of animals we 

 often witness a suspension of the functions 

 under special external circumstances, which, 

 although not amounting to the extent found 

 amongst the Infusoria, would yet prepare us 

 to admit a far more intense degree of the same 

 phenomenon amongst those beings in which 

 animality was less decided, and the vegetative 

 functions more predominant. There is no 

 necessity to regard the condition of desicca- 

 tion in which those animals may be placed as 

 one of death. The conditions of the exist- 

 ence of the vitality of the animal, whatever 

 they may be, are undoubtedly secured in this 

 state, and the' conditions of the activity of this 

 vitality are alone withdrawn. 



Although many of the species of Polygas- 

 tria are as large as the Rotifera, the structure 

 of the latter is much more easily discernible, 

 on account of the transparency of the lorica, 

 or shield, in which they are enclosed, and the 

 distinctness of their individual organs. The 

 external covering, though always clear like 

 crystal, has varying degrees of density, in 



A single, continuous, ci- 

 liated wheel. (MONO- 

 TROCHA.) 



entire. 



CHA.) 



crenated. 



TROCHA.) 



Many-parted 



A compound, or divided, 

 ciliated wheel. (SO- 

 ROTROCHA.) I Two-parted wheels. (Zy-j Is aked. 



I GOTROCHA.) j Loricated. 



some instances forming a horny kind of case, 

 insusceptible of movement, and, in others, a 

 skin susceptible of transverse corrugations. 

 Into this dense external membrane the 

 animal is capable of drawing in its tail and 

 rotatory organs; hence this class of animals 

 has been called Systolides. In none of the 

 species does there appear to be a deposit of 

 earthy salts, either in the skin or other parts 

 of the body.* This will account for the fact, 

 that few or none of the Rotifera have been 

 found in a fossilised state. Those forms 

 alone of the Polygastria have been dis- 

 covered in the chalk and subsequent forma- 

 tions, which, in their living state, possess a si- 

 liceous or calcareous skeleton. 



In the classification of the Rotifera we 

 shall follow Ehrenberg, as no separate ar- 

 rangement of these creatures existed previous 

 to his profound investigation of their struc- 

 ture ; and although other attempts have been 

 made, since the appearance of his work, on the 

 Infusoria, none of them seem better adapted 

 for the purposes of further inquiry. At the 

 same time we would, with the utmost diffi- 

 dence, express our doubts as to the correct- 

 ness of much of the terminology employed by 

 Ehrenberg, implying, as it frequently does, 

 views of the structure and functions of the 

 parts of these animals which the facts them- 

 selves, so remarkably correctly observed, do 

 not always seem to warrant. The following 

 is a table of the eight families of Rotifera 

 according to Ehrenberg : 



Icthydina. 

 (Ecistina. 



Megalotrochcea. 

 Floscularia. 



Hydatincea. 

 Euchlanidota. 

 Philodincea. 

 Brachioncea. 



Naked. 



wheels.! Naked. 



j Loricated. 



It will at once be seen that this is an exceed- he is not unaware of the defects of this ar- 

 ingly artificial arrangement ; for although the rangement, and that he has pointed out that 

 rotatory organs are the most striking external both the structure of the alimentary canal, 

 character of the Rotifera, the function they per- 

 form does not seem to be of that fundamental 



and even the teeth and jaws, would afford 

 characters by which the species might be 



importance in the economy of the animal, so arranged. Dujardin, in a recent work on the 



that a change in their form would be attended 



with corresponding changes in their general 



structure. In fact, in this arrangement, forms 



Infusoria, proposes the four following fami- 

 lies : 



1. Rotifers having the posterior part of 



are separated which are nearly related by the their bodies fixed. Examples : Floscularia, 

 affinities of more important organs. In the Stephanoceros. 



next place, the families are arranged accord- 2. Rotifers having but one means of loco- 

 ing as they are naked (panzerlose), or loricated motion, that of the vibratile cilia, and which 

 (gepanzerte). The condition of the integu- are consequently always swimmers. Exam- 

 ment here employed as a means of classifica- pies : Ptygma, Lacumolaria, Melicerta. 

 tion, cannot be regarded as absolute; and 3. Rotifers which have two modes of loco- 

 there are species which it would be difficult motion : one creeping like the leech, the other 

 to refer to either group. Some of the 

 species secrete around them an external tube, 

 in which they dwell, as Stephanoceros ( <?g. 

 292.) and others, which is an entirely different 

 thing from the hardened integument .called 

 by Ehrenberg the lorica, or shield, and yet 

 these are classed as a loricated family. It is, 

 however, but due to Ehrenberg to state that 



swimming as the last. This family includes 

 the largest number of genera, as Brachionus, 

 Dinochdris, Plerodina, Salpina, Lepadella, 

 Euchlanis, &c. 



* Ehrenberg states that the remains of some 

 Rotifera having been chemically examined; they 

 were found to contain phosphate of lime, which he 

 supposes was deposited in their jaws and teeth. 



