ROTATORIA. 



[ 557 ] 



ROTATORIA. 



but nearly always a rounded muscular giz- 

 zard containing the jaws and teeth. In the 

 pharynx are occasionally seen two undulating 

 lines, presenting a flickering appearance, the 

 indications of cilia or undulating membranes. 

 The jaws are constructed mostly after two 

 forms. In one of these, they consist of two 

 knee-shaped pieces (PI. 34. fig. 24), to the 

 posterior portion of which muscles are at- 

 tached, 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 (PI. 34. 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 (PI. 34. 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 arrangement. 



The alimentaiy canal is usually short and 

 straight, but sometimes curved. Its walls 

 are very thick and lined with ciliated epithe- 

 lium. The stomach forms a distinct expan- 

 sion (PI. 34. fig. 27 c) ; this is succeeded by 

 an intestine, the termination of which cor- 

 responds to a cloaca, receiving the expelled 

 contents of the reproductive organs and so- 

 called water-vessel system, and opening at 

 the base of the foot. In some Rotatoria, a 

 second expansion or stomach is situated 

 below the upper one. 



The walls of the stomach and intestine 

 frequently contain brown or yellow cells, 

 representing a liver. And at the commence- 

 ment of the stomach are two or more csecal 

 appendages, probably corresponding to a 

 pancreas (PI. 35. figs. 14, 34). 



Vascular system. — Distinct blood-vessels 

 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. 34. fi.g. 18 a; 

 PI. 35. fig. 14 b). Anteriorly, these vessels 

 give oiF branches, the terminations of which 

 are not well known. By some they 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. 34. fig. 18 a; PI. 35. fig. 14 c), which 

 exhibit a flickering appearance from the 

 action of cilia connected with them. Pos- 

 teriorly, the tubes terminate in an actively 

 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 considered 

 them as connected anteriorly with a certain 

 projecting tubular organ (PI. 35. fig. 14 «), 

 situated usually in the cervical region (PI. 34. 

 fig. 3; PI. 35. fig. 17), denominated the 

 calcar or respiratory tube, also viewed as an 

 antenna, and terminated by a retractile tuft 

 of non-vibratile cilia (PI. 35. fig. 5 a). 



Beneath the integument of the Rotatoria, 

 a kind of irregular circulation, varying with 

 the motions of the body, or a simple mole- 

 cular movement of minute granules, has been 

 noticed. These granules are probably situ- 

 ated in the abdominal cavity ; in which also 

 sarcodic globules, sometimes free, at others 

 connected by filaments, have been observed. 



Reproduction, — The Rotatoria are propa- 

 gated by means of sexual organs, division or 

 gemmation being unknown in them. They 

 were formerly regarded as hermaphrodite ; 

 but it is probable that they are unisexual, 

 and spermatozoa have been detected in at 

 least one species. The female organs consist 

 of one or two longer or shorter ovarian sacs 

 or ovaries, situated towards the posterior end 

 of the body in the abdominal cavity, the 

 oviduct terminating in the cloaca, or at a 

 distinct vulva. The ova are of an oval form, 

 and are sometimes smooth externally and 

 soft ; at others they correspond with the 

 winter-ova, being larger, darker, and the 

 outer coat thick, and hairy or tubercular. 



A penis (retracted foot?) has been de- 

 scribed as existing in the males. 



The ova sometimes remain adherent to 

 the cloaca for a time, and in a few instances 

 they are hatched within the ovary. 



Many of the Rotatoria are remarkably 

 tenacious of life, and some of them are stated 

 to have revived after having been kept dry 

 for several years. 



The families of the Rotatoria are thus 

 distinguished : — 



Ciliated margin of rotatory disk simple or continuous. 

 Margin entire. Holotrocha. 



Carapace absent 1 . Ichthydina. 



Carapace present 2. (Ecistina. 



Margin undulate or excised. Schizotrocha. 



Carapace absent 3. Megalotrochsea. 



Carapace present 4. Floscularieea. 



Rotatory disk divided or multiple. 

 Divided into several parts. PolytrocJia. 



Carapace absent 5. Hydatinsea. 



Carapace present 6. Euchlanidota. 



Divided into two parts. Zygotrocha. 



Carapace absent 7. Philodinsea. 



Carapace present 8. Brachionsea. 



See Albertina. 



They are found wherever water exists, 

 provided it be not in a state of putrefaction; 



