ROTATION. 



ROTATORIA. 



rotation in Vallisneria, so that the proto- 

 plasm is moved on in waves ; but the pri- 

 mordial utricle finally dissolves, and the 

 movement ceases. Passing an electric cur- 

 rent through the cell stops the current for 

 a time ; but it recovers itself, just as occurs 

 after any mechanical interference. If several 

 cells are injured by cutting or pricking, the 

 whole rotation stops in young plants, but it 

 gradually returns as before in the uninjured 

 cells. Pressure interrupts or stops the mo- 

 tion for a time only ; when removed, the 

 current is gradually restored; but actual 

 injury to the cell stops it for ever. 



The rotation which takes place between 

 the external surface of the green layer and 

 the outer cell-membrane in Closterium and 

 other DESMTDIACE^ appears to be of the 

 same kind as the above. 



The circulation in reticular currents, first 

 observed by Brown in the hairs of the 

 stamens of Tradcscantia, appears to exist 

 far more extensively, if it be not even a uni- 

 versal phenomenon. It has been observed 

 in the Confervoideae, Fucoideae, Florideae, 

 Lichens, Fungi, Hepaticae, Equisetaceae, 

 Lycopodiaceae, and Ferns, and in the most 

 varied families of Flowering plants. It is 

 seen most easily in young tissues, especially 

 such as can be prepared readily without 

 much mechanical injury,; for example, in 

 hairs, cells of the pulp of fruits, cells of the 

 germen of Onagraceae, of the labellum of 

 Orchids, &c. It generally exhibits the fol- 

 lowing characters : In the middle or at one 

 side of the cell occurs a large heap of pro- 

 toplasm, in which is imbedded the nucleus ; 

 from this protoplasm more or less slender 

 filaments run out over the cavity of the cell, 

 and as these contain numerous fine granules, 

 a flowing movement which takes place be- 

 comes evident by the change of place of the 

 granules. Attentive examination shows that 

 these flow out from the central mass and 

 return to it, and, moreover, that the cur- 

 rents change their form and direction, and, 

 lastly, that the nucleus itself moves. This 

 rotation cannot be observed in very young 

 cells when the cavity is densely filled with 

 protoplasm ; but Hofmeister states that he 

 has seen the entire primordial utricle rotate 

 in the special parent cell of the spore of 

 Phascnm cuspidatum. As the young cells 

 increase in size, vacuoles are formed in the 

 protoplasni,filled with watery sap ; and these 

 enlarging and becoming confluent, leave the 

 protoplasm in the form of a reticulated 

 mass. 



The cause of the motion is evidently 

 related to the movements exhibited by free 



Srotoplasmic bodies, such as ZOOSPORES, 

 PERMATOZOIDS, the free filaments of Os- 

 CILLATOHIA, &c. It has been well com- 

 pared with the movements of the body of 

 Amoeba, which bear considerable resem- 

 blance to some kinds of the reticular rota- 

 tion. 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 actual rotation or movement in a 

 definite direction is the result of the con- 

 fining cell-wall on the contracting and ex- 

 panding protoplasm. It is produced in 

 Algae during cell-growth. 



The rotation in Chara may be observed 

 by simply placing portions of the plant on a 

 slide in water. The unincrusted 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 ob- 

 served. Hairs are frequently more or less 

 covered with a viscid secretion, which re- 

 tains 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, Tr. Soc. Arts, xlviii. ; Mic. 

 Trans. ; Slack, Tr. Soc. Arts, xlix. ; Du- 

 trochet, Compt. Rend. 1837, 775 ; Becque- 

 rel, ibid. 784 ; linger, Sitzungsber. Wien. 

 Ak. viii. 32 ; Mohl, Sot Zeit. iv. 73 ; Ann. 

 N. H. xviii. 1 ; Hofmeister, Very. Unters. 

 73; Osborne, Mic. Jn. iii. 54; Branson, 

 ibid. iii. 260; Wenham, ibid. iii. 250 ; Hen- 

 frey, Ann. N. H. 3, i. 419; Reichert, Ann. 

 N.H. 1867, xix. 10; Beale, How $c. 4th 

 edit. 165 ; Carpenter, Microscope ; Henfrev- 

 Masters, Bot. 551. 



ROTATO'RIA or ROTIF'ERA. A 

 Class of the ANIMAL KINGDOM. 



Char. Microscopic, transparent animals, 

 living in fresh or in salt water ; legs absent ; 

 anterior portion of the body furnished with 

 one or more retractile, often lobed disks, 

 upon which are placed usually vibratile 

 cilia, when in motion presenting the appear- 

 ance of one or more revolving wheels ; ali- 

 mentary canal usually distinct, with a den- 

 tal apparatus, and two orifices ; reproduction 

 by ova. 



Body covered with a firm and usually 

 smooth skin or integument, sometimes pre- 



