29* Account of Professor Ehrenherg^s 



animals of the class of Polygaslrica. According to his observa- 

 tions, these organs are constantly and invariably present in those 

 species which have been discovered to possess them, even under 

 very varied circumstances, insomuch that he has derived from 

 them distinctive characters of itouch value in his systematic ar- 

 rangement. MO . if-j .v> 



The eyes of the Rotatoria appear as one, t\vo, often three, or 

 even more spots, usually of a red colour, placed at the fore-part 

 of the animal, either before the rotatory organs on what might 

 be named the forehead, or immediately behind them, on a part 

 of the body which might be compared to the nucha or nape of the 

 neck in other animals ; or they may occupy both these situations 

 (Plate I. Fig. 11.) They appear, according to Dr Ehrenberg, 

 to be immediately connected with the nervous system ; for the pos- 

 terior one is always placed either at the point where the summit 

 of the nervous arch or loop, arising from the cerebral ganglion, 

 touches the skin, or, when the loop is wanting, directly over the 

 ganglion itself, and the anterior or frontal eyes always occupy a 

 situation which corresponds with the points where, as is seen in 

 the Hydatina senta, two filaments proceeding from the nervous 

 loop in the neck reach the region of the forehead. 



That these organs are in reality the eyes of the infusorraV W 

 rendered extremely probable by the fact of their being so ex- 

 tensively prevalent among those animals, — by their great regula- 

 rity and constancy, — and by their obvious connexion with what 

 appears to be a nervous apparatus. This opinion is corro- 

 borated by the fact that, in most cases, they contain a very 

 highly coloured pigment, which, on crushing the little animals 

 between two plates of glass, is effused in the form of a finely 

 granulated mass, bearing miich resemblance to the pigment iri 

 the eyes of other animals. "^ 



As a further proof that the infusoria are provided with atr oi*-* 

 gan of vision, Dr Ehrenberg adduces the great precision witfi 

 which they execute their movements, seize on their prey, or 

 otherwise direct themselves towards particular objects; nay, 

 these actions seem so decidedly to require the aid of vision for 

 their performance, that he is induced to think that faculty may 

 be probably possessed by those species which are destitute of 

 coloured eyes, and that the function may in such cases be exer- 



