144 



THE ROTATOrJA. 



^134, 



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

 crenulate, but entire. ''' With those whose organs are more numei-ous, but 

 smaller, this appearance is not observed/-^ 



With Floscidaria, and Stephaiioceros, the rotatory organs have quite a 

 different 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. But 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 



NERVOUS 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 certain, however, that in all, there is, as a nervous centre, a 

 group of cervical ganglia, from which pass off' threads in various direc- 

 tions.^^' 



1 Conochilus, Philodina, and Actinurus. 



2 Hydatina, Notommuta, Synchaeta, andZ>ig"- 

 lena. 



3 See Ehrenberg, Die Infusionsthierchen, Taf. 

 XLV. 



4 According to Ehrenberg, there are, at the base 

 of each ciliuin of the rotatory organs, many striated 

 muscles, which, acting antagonistically, produce the 

 motion (Abliandl. d. Berl. Akad. 1S31, p. Si). 



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 which the virbra- 

 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 these 

 animals, first took for a cerebral ganglion the gland- 



uliform body found upon most Rotatoria, and in; 

 the neck of Hydatina senta, and Notommata col- 

 laris (Abhaudl. d. Bcrl. Akad. 1830, p. 52, Taf. 

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

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

 mentioned with Hydatina, Synchaeta, 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, Notommata, and Diglena, he- 

 has regarded as a nervous loop, the two filaments 

 which pass off from the cerebral ganglion, and go to 

 the cervical respirntory orifice. Finally, he refers 

 to the sensitive systi-m, a wliite sacculus, single or 

 double, and situated behind the cerebral ganglion, 

 with Notommata, Diglena, and Theorus (Die 

 Infusionsthierchen, p. 425). GrantKi description of 

 the nervous system of the Hydatina, as being 

 composed of many ganglia and a ventral cord, 



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

 speaks of two kinds of cilia with Flo.icu/aria ; " one 

 of the usual short vibratile kind, covering the inte- 

 lior of the alimentary lube ; the other extremely 



long and filiform, of uniform thickness, and not 

 Vibratile under ordinary circumstances." They ar» 

 slowly moved, being spread out by the contractile 

 substance of the lobes of the rotatory organ. — E». 



