"§>*§> 132, 133. THE ROTATORIA. 143 



the annular sulcations of the skin, partial, or over its whole extent, give 

 the body an articulated aspect/-^ Many others have a skin so hard and 

 gtiif, as to be like a carapace/^^ 



CHAPTER II, 



MUSCULAR SYSTEM AND LOCOMOTIVE ORGANS. 



§ 132. 



The muscular system of the Rotatoria is quite distinct in many parts of 

 the body. There can at once be observed, distinctly separated from the 

 general parenchyma, unstriated muscles, of which some are transversely 

 annular, and many others narrow and longitudinal.^^' The first, subcuta- 

 neous and widely separated from each other, are usually upon the borders 

 of the segments of the body. The second, divisible into dorsal, ventral and 

 lateral portions, arise from the internal surface of the skin, and are inserted 

 at the cephalic or opposite extremity.^-' 



The posterior extremity of those species which move freely, has two stiff 

 points of variable length, which are moved as tentacles by two cylindrical, 

 or clavate, caudal muscles. Some have long, movable bristles or pedicles, 

 by which they row along or move by quick leaps.® 



§ 133. 



The prominent characteristic of the Rotatoria is the retractile, vibratile 

 apparatus at their cephalic extremity, known as the rotatory organs. By 

 these, they swim freely about, revolving upon their axis, or, when at rest, 

 produce vortex-like motions of the water. The form, number, and arrange- 

 ment of these organs varies much according to the genera, and may be 

 «sed even to characterize families. 



The rotatory organ is either single, double, or multiple. Often it con- 

 sists of a disc, supported by a pedicle of variable length, upon whose bor- 

 ders are successive rows of regularly-arranged cilia, the motion of which 

 gives the appearance of rotation to the disc itself. This apparent motion 



2 With Conochilus, Megalotrocha, Lacinula- cles of Euch/anis triquetra are transversely stri- 

 ria, Brachionus, Noteus, Sr/uamena, Notom- ated like those of the higher animals (Die Infus- 

 mata, and Stephanops, the tail is transversely ionsthierchen, p. 462, Taf. LVII. fisr. 8). 



marked or articulated. With many species of Hy- 2 For the muscles of the Rotatoria in general, see 



datina, Rotifer, Philodina, Actinurus, and Eos- Ehrenberg, loc. cit. and his description of the Hy- 



phora, not only the caudal extremity, but the whole datina senta, in the Abhandl. d. Bed. Akad. 1830, 



body, is regularly segmented, and capable, espe- p. 47. 



cially at the posterior extremity, of being intussus- 3 Many Rotatoria use their caudal pincers as a 



cepted or drawn out, like a telescope. fulcrum when creeping along. Philodina move» 



3 A solid carapace, like the shell of Daphnia, is along in a leech-like manner, using its mouth and 

 found with Brachionus, Anuraea, Noteus, Salpi- tail as suckers. Polyarthra has many bundles of 

 na and Eiichlanis. bristles upon the sides of its body, which it uses as 



1 The muscles are smooth when at rest, but when oars. Triarthra has under the throat and at the 

 contracted, they appear more or less distinctly pli- posterior extremiiy of the body, long stiff bristles, 

 cated transversely. The assertion of Ehrenberg articulated with the body, and by which these ani- 

 ls therefore remarkable, that the longitudinal mus- mals can leap like a flea. 



