INFTT80KIAL ANIMALCULES. 81 



to it a respiratory office. He adda, " The supposed vascular ramifi- 

 cations upon it, are neither more nor less than the muscular fibriUae 

 by which the contractions are effected." 



Section XXIII. — Of the Organs of Sensation and Nervous System 

 of Rotatoria. — The Rotatoria arc not considered to possess a true ner- 

 vous system, but ia many of the species, having eyes, there appears 

 one or two masses attached to them, which Ehrenberg thinks are 

 similar to nervous ganglia and nervous fibrillse. The eyes vary in 

 number ; they are usually of a red colour ; in some they are placed 

 upon a ganglion, and are freely moveable beneath the transparent 

 superficial envelope of the body. 



The visual organs are of small size, but always sharply defined, 

 and, it would appear, invested with a homy capsule in some cases. 

 The firm capsule is observable in ConocJiilus, Rotifer^ and Philodina. 

 Dujardin opposes the opinion of the visual character of these red 

 specks in Rotatoria, chiefly on account of their not uncommon dis- 

 appearance in the adult state. But as Siebold remarks, an objection 

 raised on this circumstance is not valid, since a similar phenomenon 

 is known to take place in the adult condition of parasitic Crustacea, 

 the visual character of whose eye- specks or ocelli is not questioned. 

 Moreover the coloured specks in Rotatoria are sharply defined, and 

 in some cases at least, furnished with capsules, thus differing totally 

 from the non-capsular, ill-defined pigment masses of Foli/gastrica, 

 called eyes. 



It is doubtftd, however, Siebold remarks, whether the dispro- 

 portionately large specks, described as eyes by Ehrenberg, in Notom- 

 mata forcipata, Synchcct-a haltica, in Cycloglen<i and Eosphoi'a, are other 

 than loose aggregations of coloured particles. 



The same author says " there is, in Rotatoria^ a constant group of 

 ganglions in the neck, regarded as the central organ of the nervous 

 system, from which, nerve-cords radiate on all sides." Over this cere- 

 bral centre, the organs of vision are seated, and receive fi-om it their 

 special nerve fibres. 



The variable relative position of the eyes is detennined by that of 

 the ganglions. The position of the former may be on the neck,- — i. e. 

 posterior to the base of the rotaiy organs, or on the fore-part of the 

 head, or even in advance of the rotary apparatus. 



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