ROTATORIA. 



[ 670 ] 



ROTATORIA. 



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 cilia, 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 

 extended 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 longitudinal and circular muscu- 

 lar bands are present ; and they sometimes 

 present transverse striae. 



The rotatory disks or wheel-organs vary 

 greatly in structure, the varieties forming 

 characters of the families and genera. 



Their margin is usually furnished with 

 one or two rows of vibratile cilia ; some- 

 times these are replaced by bundles of non- 

 contractile elongate cilia (PI. 43. fig. 32), 

 or the rotatory organ is divided into ten- 

 tacle-like processes, upon which cilia are 

 placed (PL 44. 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 pro- 

 boscis (PI. 43. fig. 1). 



The nervous system is not well known. 

 It appears to consist of a ganglion and of 

 branches given off in various directions. 



In many of the Rotatoria, eyes are pre- 

 sent, mostly red. These appear to have a 

 cornea and a lens. They sometimes dis- 

 appear in the adult animals ; and as their 

 number, position, &c. are used as charac- 

 ters, when absent in the adults, they must 

 be looked for in the young or the ova, 

 either within tlie carapace or adherent to 

 the body. 



Alimentary apparatus. Behind the mouth 

 is sometimes a distinct conical pharynx, 

 but nearly always a rounded muscular giz- 

 zard containing the jaws and teeth. In the 

 pharynx are occasionally seen two undula- 

 ting lines, presenting a flickering appearance, 

 the indications of cilia or undulating mem- 

 branes. The jaws are constructed mostly 

 -after two forms. In one of these they con- 



sist of two knee-shaped pieces (PI. 43. fig. 

 24), to the posterior portion of which 

 muscles are attached, whilst the anterior, 

 which passes inwards at a right or obtuse 

 angle to the former, ends in a single point 

 or in several teeth (fig. 26). In the other, 

 the jaws have the form of stirrups (fig. 17), 

 with their bases turned towards each other, 

 upon which two or more teeth are placed. 

 A third single or compound intermediate 

 piece forms a support (figs. 24, 26), upon 

 which the food acted upon by the jaws 

 is triturated. In some species the jaws 

 and teeth are very complex in their ar- 

 rangement. 



The alimentary canal is usually short and 

 straight, but sometimes curved. Its walls 

 are very thick, and lined with ciliated epi- 

 thelium. The stomach forms a distinct 

 expansion (PI. 43. fig. 27 c) ; this is suc- 

 ceeded by an intestine, the termination of 

 which corresponds to a cloaca, receiving the 

 expelled contents of the reproductive organs 

 and so-called water- vessel system, and open- 

 ing at the base of the foot. In some Rota- 

 toria a second expansion or stomach is situ- 

 ated below the upper one. 



The walls of the stomach and intestines 

 frequently contain brown or yellow cells, 

 representing a liver ; and at the commence- 

 ment of the stomach are two or more caecal 

 appendages, probably corresponding to a 

 pancreas (PI. 44. fig. 14). 



In the male Rotatoria, the alimentary 

 canal is entirely absent. 



Vascular system. Distinct bloods 

 are apparently not present in the Rotatoria ; 

 but on each side of the body, in most of 

 them, runs a narrow straight or wavy band, 

 containing a slender vessel (PI. 43. fig. 18 a; 

 PI. 44. fig. 14 b). Anteriorly, these vessels 

 give off branches, the terminations of which 

 are not well known. By some thev are said 

 to open into the abdominal cavity, by others 

 to terminate as caeca. Attached to the walls 

 of these lateral tubes, or situated within 

 them, are pear-shaped or oval corpuscles 

 (PI. 43. fig. 18 a; PL 44. fig. 14 c), which 

 exhibit a flickering appearance from the 

 action of cilia connected with them, and 

 which open into the cavity of the abdomen. 

 Posteriorly, the tubes terminate in an ac- 

 tively contractile sac, which opens into the 

 cloaca. In regard to their function, these 

 tubes have been variously viewed as water- 

 vessels, testes, and kidneys. Ehrenberg con- 

 sidered them j).s connected anteriorly with 

 a certain projecting organ (PL 44. fig-. 14 a 



