$$ 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 
stiff 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 
used 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- 
ria, Brachionus, Noteus, Squamelia, Notom- 
mata, and Stephanops, the tail is transversely 
marked or articulated. With many species of Hy- 
datina, Rotifer, Philodina, Actinurus, and Eos- 
phora, not only the caudal extremity, but the whole 
‘body, is regularly segmented, and capable, espe- 
cially at the posterior extremity, of being intussus- 
cepted or drawn out, like a telescope. 
3 A solid carapace, like the shell of Daphnia, is 
found with Brachionus, Anuraea, Noteus, Salpi- 
na and Euchlanis. 
1 The muscles are smooth when at rest, but when 
contracted, they appear more or less distinctly pli- 
cated transversely. The assertion of Ehrenberg 
4s therefore remarkable, that the longitudinal mus- 
cles of Euchianis triquetra are transversely stri- 
ated like those of the higher animals (Die Infus- 
ionsthierchen, p. 462, Taf. LVITI. fig. 8). 
2 For the muscles of the Rotatoria in general, see 
Ehrenberg, loc. cit. and his description of the Hy- 
datina senta, in the Abhandl. d. Berl. Akad, 1830, 
p. 47. 
83 Many Rotatoria use their caudal pincers as a 
fulcrum when creeping along. Philodina moves 
along in a leech-like manner, using its mouth and 
tail as suckers. Polyarthra has many bundles of 
bristles upon the sides of its body, which it uses as 
oars. Triarthra has under the throat and at the 
posterior extremiiy of the body, long stiff bristles, 
articulated with the body, and by which these ani- 
mals can leap like a flea. 
