^<J 135, 136. 



THE ROTATORIA. 



145 



§ 135. 



Beside the sense of touch, apparently located chief! j in the rotatory 

 organs and their 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 tlie 

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



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 f(jur styles projecling from the front of 

 Si/nrhaeta, are probably of the same nature. 



i The eye-speclc is simple with Enchlanis, No- 

 tomviala, Synckavta, Vycto^lcna, and Brachio- 

 nux ; double with Conorhi/vf!, Mcsalolrocha, 

 Dielena, Rotifer, and Philodina ; with Eosphora, 

 there are tlu-ee, aii.l with Sf/uamcl/a, four ; while 

 Hydatina, Entrroplea, Pti/^ura, Tubicolaria, 

 and the adult Fiosculariae, have none at all. 



■5 Ehrenbers:, who was the fir^;t to regard these 

 red dots as eyes, has given their i;itimate structure 

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



regretted since Dujardin has not regarded them 

 as visual organs (Infusoires, p. 591). I1-: su|>- 

 ports this view by the fact that they di3a))peai- willi 

 the adult individual ; but this objection will ajipear 

 valueless when it is remembered thit this is also 

 true of certain parasitic Crustacea. At all events, 

 the small ocular dots of Conocki/iifs, Rotifer, and 

 Philodina, are nicely-defined organs surrounded 

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

 ferent ft'om the ddfused masses of red pigment 

 which Ehrenberg has erroneously taken for eyes 

 with the Infusoria. The disproportionate size of 

 the red dots wliich Ehrenberg (Die Infusionsthier- 

 chen, Taf. LI. IJII. LVI.) has figured will] Notom- 

 mata foTcipata, Syncliae.la baltica, Cyclog/ena, 

 and Eosp/iora, lead one to sup])0se that they are 

 only collections of pigmentary granules. 



* [ § 13-t, note 1. J Gossf (Ann. X;it. TTist. 1850, p. 

 21) describes the nervous system of Asplanchna 

 priodonta as follows : " Each of the three eyes rests 

 on a mass that appears ganglionic ; thi; clubbed 

 masses at the lateral apertures are probably of the 

 same char?.cter ; 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 Kntwickelungsgeschichtc 

 der Lacinularia socialis, in Siebold and K6llikcr''s 

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

 liar nervous system with Lacinularia, consisting 

 of : " 1. A ganglion behUid the pjiarynx, comi)osed 



13 



of foui' liip'lar cill; with their [u'ocesses. 2. A gan- 

 glion at the beginning of the caudal prolongation, 

 similarly composed of four larger ganglionic cells 

 and their processes." Uut, that these parts belong 

 to the nervous system, ai>iicars 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 simi)ly from the histological 

 constitution of the parts, and from the imi)assibility 

 of making anything else out of them, unless in- 

 deed, organs are to be named according to oar 

 mere will and pleasure." — Kd. 



