ROTATORIA. 



[ 556 ] 



ROTATORIA. 



parent-cell of the spore ofPhascum cuspida- 

 tum. As the young cells increase in size, va- 

 cuolesare formed in the protoplasm, filled with 

 watery sap, and these enlarging and beco- 

 ming confluent, leave the protoplasm in the 

 form of a reticulated mass. 



The cause of the motion is quite unex- 

 plained, but it is evidently related to the 

 movements exhibited by free protoplasmic 

 bodies, such as ZOOSPORES, SPERMATO 

 ZOIDS, the free filaments of OSCTLLATORIA, 

 &c. It has been stated to be dependent on 

 the action of cilia, but we believe this is to- 

 tally erroneous, and that it is rather referable 

 to a common cause with the motion of cilia 

 themselves. It has been well compared 

 with the movements of the body of Amoeba, 

 which bears considerable resemblance to 

 some kinds of the reticular rotation. The 

 relation existing here is further borne out 

 by the fact of pulsating vacuoles existing in 

 Volvox, Gonium, &c., just like those in the 

 Infusoria. 



The rotation in Chara may be observed 

 by simply placing portions of the plant on a 

 slide in water. The unencrusted species are 

 of course most favourable, but the growing 

 points of the others are tolerably transpa- 

 rent. In Vallisneria, detached fragments of 

 leaves, or even horizontal sections of the 

 leaf, may be used ; in Anacharis entire leaves 

 or sepals may be detached and observed. 

 Hairs are frequently more or less covered 

 with a viscid secretion, which retains air- 

 bubbles about them; in such cases, it is 

 often useful to dip them for an instant in 

 alcohol, and then place them in water. 



BIBL. Varley, Trans. Soc. of Arts, xlviii. 

 (1832), Mic. Trans. ; Slack, Trans. Soc. 

 Arts, xlix. ; Dutrochet, Comptes Rendus, 

 1837. p. 775; Becquerel, ibid. p. 784; 

 Meyen, Pflanzenphys. ii. p. 206 ; A. Braun, 

 Richtungsverhaltnisse du Saftstrome, Berlin 

 Bericht. 1852 ; Goppert and Cohn, Bot.Zeit. 

 vii. p. 665 (1849) ; Unger, Sitzbericht d. 

 Wien. Akad. viii. p. 32 ; Mohl, Bot. Zeit. 

 iv. p. 73 (1846), Ann. Nat. Hist, xviii. p. 1; 

 Hofmeister, Vergleich. Unters. p. 73 ; Os- 

 borne, Mic. Journal, iii. p. 54 (1 854) ; Bran- 

 son, ibid. iii. p. 260 (1855); Wenham, ibid. 

 p. 250. 



ROTATORIA or ROTIFERA. A class 

 of the Animal Kingdom. 



Char. Microscopic, transparent, aquatic 

 animals; legs absent; anterior portion of 

 the body furnished with a retractile, often 

 lobed disk, upon which are placed usually 

 vibratile cilia, when in motion presenting the 



ajypearance of one or more revolving wheels ; 

 alimentary canal usually distinct, with a den- 

 tal apparatus, and two orifices ; reproduc- 

 tion by ova. 



Body covered with a firm and usually 

 smooth skin or integument, sometimes pre- 

 senting indications of segments ; often more 

 or less enclosed in a carapace (CARAPACE), 

 which is either secreted by the skin, by the 

 alimentary canal, or by a special secreting 

 organ. In some species the skin is fur- 

 nished with hairs or rigid bristles. 



In most, there is a tail-like process at the 

 posterior end of the body called the foot-like 

 tail, tail-like foot, or false foot ; this is 

 jointed, and can often be contracted and ex- 

 tended like a telescope ; it does not form a 

 direct prolongation of the end of the body, 

 but arises from and is situated upon the 

 ventral aspect. It is often terminated by a 

 suctorial disk, or a pair of claw- or toe-like 

 processes. 



Distinct muscular bands are present, 

 longitudinal, circular, &c.; these sometimes 

 present transverse striae, but it is doubtful 

 whether they agree with those of the fibres 

 of the higher animals. 



The rotatory disk or wheel-organ varies 

 greatly in structure, the varieties forming 

 characters of the families, &c. 



Its margin is usually furoished with one 

 or two rows of vibratile cilia; sometimes 

 these are replaced by bundles of non-con- 

 tractile elongate cilia (PI. 34. fig. 32), or the 

 rotatory organ is divided into tentacle-like 

 processes, upon which cilia are placed (PI. 

 34. fig. 25). 



The rotatory disk is the principal organ 

 of motion, by means of the cilia of which 

 the animals swim through the water ; some 

 of the Rotatoria, however, move in a leech- 

 like manner, by alternately fixing the 

 toe-like processes and the anterior end of 

 the body, which in some forms a kind of 

 proboscis (PI. 34. fig. 1). 



The nervous system is not well known. 

 It appears to consist of a cervical ganglion, 

 and branches given off in various directions. 



In many of the Rotatoria, eyes are present, 

 mostly red. These appear to have a cornea 

 and a lens. They sometimes disappear in 

 the adult animals, and as their number, 

 position, &c. are used as characters, when 

 absent in the adults, they must be looked 

 for in the young or the ova, either within 

 the carapace or adherent to the body. 



Alimentary apparatus. Behind the mouth 

 is sometimes a distinct conical pharynx ; 



