ROTIFERA. 



411 



Projecting from the upper part of the ex- 

 ternal tegument, in many species, is a little 

 process, which Ehrenberg calls a spur, or 

 siphon {Jig. 299. d), and which he thinks is 

 connected with the function of respiration, 

 and therefore calls it a respiratory tube. It 

 corresponds with an orifice in some species 

 (Jig. 293. g), which Ehrenberg calls therespira- 

 tory orifice. He has also hinted that they 

 may be connected with the reproductive func- 

 tion. Two of these organs are seen in some 

 of the Notommata and other genera, and they 

 are sometimes covered with cilia. Dujardin 

 thinks that they resemble more closely the 

 palpi and antennas of the Entomostraca. 



The rotatory organs, or wheels, must be 

 also regarded as a portion of the tegumentary 

 system. They are fleshy retractile lobes, 

 covered with vibratile cilia, capable of being 

 contracted or expanded at the will of the 

 animal. The movement of the cilia when the 

 lobes are expanded gives the appearance of a 

 wheel moving upon its axis, an appearance 

 which was a source of much wonder to the 

 earlier observers of these creatures. In addi- 

 tion to the vibratile cilia, there are frequently 

 found, on the rotatory lobes, setae, or bristles, 

 which have not the power of moving. This 

 is the case in Floscularia, if, indeed, the 

 organs called rotatory in that genus are truly 

 homologous with the rotatory organs in other 

 species. The true homologue of the rotatory 

 apparatus in Floscularia appears to us to be 

 seated within the external ciliated lobes, where 

 an evidently active motion is constantly going 

 on. The form of the lorica varies greatly ; in 

 some species it is flat and depressed, as in 

 Pterodina and Monostyla ; in others it is pris- 

 matic, as in Mastigocerca, or gaping, as in 

 Euchlami {Jig. 294.). Some species, as Ste- 

 phanoceros (Jig. 292.), Floscularia, Melicerta, 

 and others, have a soft skin, very contractile, 

 which secretes externally a case, and which 

 Ehrenberg calls a lorica ; but this is essen- 

 tially a different organ from the lorica. Where 

 this case occurs, it seems to stand in the same 

 relation to the animal as the Polypidon of 

 the zoophytes. The animals which form 

 these cases are also fixed, and retract their 

 bodies within their case in the same manner 

 as the Polypiferae. The Floscularia may be 

 compared to the Hydroid Polyps, while Ste- 

 phanoceros, with its ciliated tentacula-like pro- 

 cesses, would appear to have a relation with 

 the Ascidoid polyps. 



Motory system. As the movements of 

 the Rotifers are rapid and various, so we find 

 their muscular system complicated. The 

 principal organs of locomotion are the rota- 

 tory organs, by which alone the great mass of 

 the Rotifers appear to move. The move- 

 ments effected by these organs are performed 

 principally by the agency of the vibratile 

 cilia. Although no tissue has yet been dis- 

 covered in the cilia of the Rotifera and Poly- 

 gastria, Professor E. Forbes has observed 

 fibrous tissue in the cilia of a species of Me- 

 dusa?, and there can be little doubt that the 

 movements of the cilia, like those of organs to 



which muscles are attached, are of two kinds, 

 one of which is under the control of the will, 

 and the other not. In the Rotifera, the 

 vibratile cilia of the rotatory organ appear to 

 be under the control of the will of the animal. 

 The extension and contraction of the rotatory 

 apparatus is under the influence of longitudinal 

 muscular bands, which are very evident in most 

 of the species (Jig. 293. e,e,e,e ;Jig. 296. ',Jig. 

 294. b). Not only is it evident, from the action 

 of these muscles, that they are under the con- 

 trol of the will of the animal, but Ehrenberg 

 has described some of these muscles as pos- 

 sessing the striated character of the voluntary 

 muscles of animals higher in the scale of or- 

 ganisation. Euchlanis triquetra (Jig. 294. b) 

 and the species of Eosphora are those in 

 which striated muscles have been observed. 

 This fact is interesting in connection with 

 Mr. Busk's observation of the existence of 

 muscular striae in Anguinaria spathulata, a 

 form of ciliobrachiate polyps. It affords a 

 proof not only of the relation of these two 

 families, but also of both, to the articulate 

 tribes rather than to the Mollusca. Mr. Busk, 

 after the most patient research, has not been 

 able to discover the presence of striae in the 

 muscular system of the Mollusca. Not only 

 have the longitudinal bands been regarded as 

 active agents in the movement of the rotatory 

 organ, but also certain transverse bands. 

 These bands (/g.293.///,/;/g.299.g,g,g) 

 have been described by Ehrenberg as trans- 

 verse vessels. There seems to be little proof 

 that such is their office. 



In many of the Rotifers, more especially 

 the Philodinaea, the tail is employed for the 

 purposes of progression. In order to effect 

 this, it is supplied with distinct muscular 

 bands (Jig. 293. e). Muscular fibres have also 

 been described by Ehrenberg surrounding the 

 oesophagus, and apparently assisting the jaws 

 in their movements, in Conochilus (Jig* 289.), 

 Pleurotrocha, and other species. 



Digestive system. This apparatus is per- 

 haps more highly developed than any other 

 part of the Rotifera. An oral and an anal 

 orifice indicate the commencement and end of 

 this system. It is furnished with jaws and 

 teeth, an oesophagus, sometimes a distinct sto- 

 mach, and various forms of intestinal glands. 

 At the commencement of this system, we 

 find a distinct masticatory apparatus, which 

 consists generally of two semicircular pieces, 

 to each of which is attached one or more 



Fig. 300. 



Jaws of Brachionus brevissimus. (After Ehrenberg.) 



teeth, which act upon a central plate (Jig. 300. ; 

 /g.299. e;Jig. 289. o,c;/g.296. b ;fig. 292.d; 



