144 



THE ROTATORIA. 



^134. 



is quite roinarkablc with those species whose single or double disc is not 

 crenulate, but entire."^ With those whose organs are more numerous, but 

 smaller, this appearance is not observed/-' 



With Floscularia, and Stephanoccros, the rotatory organs have quite a 

 diiFercnt form. With the first, there are five or six button-like processes 

 about the mouth, covered with very long bristles ; these bristles produce 

 usually but very feeble motions, and rarely give rise to vortexes, liut Ste- 

 phanoceros reminds one much of the Bryozoa, for its rotatory apparatus con- 

 sists of five tentacle-like processes covered with vibratile cilia*" The rota- 

 tory organs differ, moreover, from the ordinary vibratile cilia of epithelium, 

 in being under the animal's control, — that is, moved or kept at rest, at 

 will.'"' 



CHAPTERS III. AND IV. 



NEKVOUS SYSTEM AND ORGANS OF SENSE. 



§ 134. 



Notwithstanding the transparency of the Rotatoria, and the distinctness 

 with which their organs are separated from each other, yet their nervous 

 system has not yet been made out with certainty, for their bodies are so small 

 that their peripheric nerves elude the microscope, and their principal nerves 

 and ganglia cannot be distinguished from the muscular fasciculi, the liga- 

 ments, and the contractile parenchyma of the body. 



It appears cei'tain, however, that in all, there is, as a nervous centre, a 

 group of cervical ganglia, from which pass oft" threads in various direc- 

 tions.*^* 



1 Conochilus, Philodina, and Actinurus. 



2 Hydatina, Notonimata, Synchaeta, and Di^- 

 lena. 



3 See Ehrenberg, Die Infusionsthierchen, Taf. 

 XliV. 



4 According to Ehrenberg, there are, at the base 

 of each cilium of the rotatory organs, many striated 

 muscles, which, acting antagonistically, produce the 

 motion (Abliandl. d. Berl. Akad. 1831, p. 34). 



But neither Dujardin (Infusoires, loc. cit. p. 

 579), nor Rymer Jones (Compar. Anat. &c. p. 

 120), has been able to perceive this apparatus. 

 The contractile parenchyma on wliich the virljra- 

 tile discs are situated, appears to be destined only 

 for the protrusion and retraction of the rotatory 

 organs.* 



1 Ehrenberg, to whom we are indebted for our 

 chief information upon the nervous system of tlrese 

 animals, first took for a cerebral ganglion the gland- 



* [ § 133, note 4.] Dobie (Ann. of Nat. Hist. 1848) 

 speaks of two kinds of cilia with Floscularia ; " one 

 of the usual short vibratile kind, covering the inte- 

 rior of the alimentary tube ; the other extremely 



uliform liody found upon most Rotatoria, and in 

 the neck of Hydatina scnta, and JYotommata col- 

 laris (Abhandl. d. Berl. Akad. ISoO, p. 52, Taf. 

 Vm. 1833, p. 189, Taf IX., and. Die Infusionsthier- 

 chen, p. 386, &c.). Besides this ganglion, he has 

 mentioned with Hydatina, Synchaita, and Dig- 

 lena, many others scattered through the anterior 

 part of the body, and connecting with the cerebral 

 one by nervous filaments. Likewise, with Enter- 

 oplea, Hydatina, Notommala, and Diglena, he 

 has regarded as a nervous loo]), the two filaments 

 which pass off from the cerebral ganglion, and go to 

 the cervical respiratory orifice. Finally, he refers 

 to the sensitive system, a white sacculus, single or 

 double, and situated behind the cerebral ganglion, 

 with Notommala, Diglena, and Theorus (Die 

 Infusiousthierchou, p. 425). GranVs description of 

 the nervous system of the Hydatina, as being 

 composed of many ganglia and a ventral cord, 



long and filiform, of uniform thickness, and not 

 vibratile under ordinary circumstances." They are 

 slowly moved, being spread out by the contractile 

 substance of the lobes of the rotatory organ. — Ed. 



