VS^ 135, 136. 



THE ROTATORIA. 



145 



§ 135. 



Beside the sense of touch, apparently located chiefly in the rotatory 



organs 



and theiu tentaculiform processes/'' these animals have also an 

 organ of vision. Usually this consists of a single or double eye-speck 

 upon the neck ; and sometimes, though rarely, of three or four red specks 

 upon the forehead.^-' These specks are usually very small, but nicely defined, 

 and covered by a kind of cornea. They are situated immediately upon the 

 cerebral ganglion, or are directly connected with it, by nervous filaments.^'' 



CHAPTER V. 



DIGESTIVE APPARATUS. 



§ 136. 



The digestive apparatus is well developed with the Rotatoria, and has 

 the following parts : 



The mouth opens into a muscular pharynx which has two horny, masti- 

 catory organs, which move laterally upon each other. Succeeding this 

 pharynx is a narrow oesophagus of variable length, which leads to a stomachal 



(Outlines, &c., p. 88, fig. 82, B.), is founded, un- 

 doubtedly, upon supposition, and not upon real ob- 

 servation.* 



1 The vibratile disc of Conochilus has upon its 

 centre,four cylindrical processes, terminating usu- 

 ally by a bristle, and quite resembling antennae. 

 The two or four styles projecting from the front of 

 Synchaeta, are probably of the same nature. 



^ The eye-speck is simple with Euch/anis, No- 

 tommata, Synchaeta, Cyc/oslena, and Brachio- 

 nus ; double with Conorhi/iis, Mesalotrocha, 

 Di^/ena, Rotifer, and Pliilodina ; with Eospliora, 

 there are three, and with Squamella, four ; while 

 Hydatina, EnteropUa, Ptygnra, Tubicolaria, 

 and the adult Floscutariae, have none at all. 



^ Ehrenber^, who was the first to regard these 

 red dots as eyes, has given their intimate structure 

 in none of his writings ; this is the more to be 



* [ § 134, note l.J Gosse (Ann. Nat. Hist. 1S50, p. 

 21) describes the nervous system of Asplanchna 

 priodonta as follows : " Each ofthe three eyes rests 

 on a mass that appears ganglionic ; the clubbed 

 masses at the lateral apertures are probably of the 

 same character ; and the interior of the body con- 

 tains a number of very delicate threads, floating 

 freely in the contained fluid, which have thickened 

 knobs here and there, especially where they anas- 

 tomose." 



Leydig (Zur Anat. und Eutwickelungsgeschichte 

 der Lacinularla socialis, in Siebold and Kolli/cer^s 

 Zeitsch. Feb'y, 1852, p. 457) describes a very pecu 

 liar nervous system with Lacinularia, consisting 

 of : "1. A gangUon behilid the pharynx, composed 



13 



regretted since Dujardin has not regarded them 

 as visual organs (Infusnires, p. 59y. He sup- 

 ports this view by the fact that they disappear with 

 the adult individual ; but this objection will apjicar 

 valueless when it is remembered that this is also 

 true of certain parasitic Crustacea. At all events, 

 the small ocular dots of Conochilus, Rotifer, and 

 Philodina, are nicely-defined organs suri-ounded 

 with a solid capsule, and appear to me wholly dif- 

 ferent from the diffused masses of red pigment 

 which Ehrenberg has erroneously taken for eyes 

 with the Infusoria. The disproportionate size of 

 the red dots which Ehrenberg (Die Infusionsthier- 

 chen, Taf. LI. LIII. LVI.) has figured with Notom- 

 Tnata forcipata, Synchaeta baltica, Cycloglena, 

 and Eosphora, lead one to suppose that they are 

 only collections of pigmentary granules. 



of four bipolar ceUs with their processes. 2. A gan- 

 glion atihe beginning of the caudal prolongation, 

 similarly composed of four larger ganglionic cells 

 and their processes." But, that these parts belong 

 to the nervous system, appears by no means posi- 

 tive ; for, as, this observer candidly observes, and 

 it is, I think, a capital comment on this whole 

 class of study : " That these cells, with their radiat- 

 ing processes, are ganglion globules and nerves, is 

 a conclusion drawn simply from the histological 

 constitution of the parts, and from the impossibility 

 of making anything else out of them, unless in- 

 deed, organs are to be named according to our 

 mere will and pleasure." — Ed. 



