168 NATURAL HISTORY 



I have also, by the aid of a superior Achromatic Micro- 

 <!Cope, satisfied myself of the existence and situation of 

 the eyes ; it will therefore be desirable to give a drawing 

 of it, with some details of the parts, in order to render 

 the account more explicit. Figure 255 represents the 

 common wheel animalcule with the wheels withdrawn, 

 and the body contracted ; the ciliated mouth furnished 

 with a cleft proboscis, or hook-shaped projection, which 

 the creature elevates or depresses at pleasure : this part, 

 however, is better shewn at figure 251, which gives the 

 upper part of the same animalcule in its elongated form. 

 Near the proboscis may be distinguished two small round 

 spots, which, if the microscope be of large angular aper- 

 ture, and free from aberration, appear of a bright trans- 

 parent red colour, if not of a dark brown, owing to the 

 want of light : these are the visual organs, and behind 

 them may be detected the two rotatory organs folded 

 within the body, the form of which constitutes one of the 

 principal features between this and the succeeding species. 

 By attentive observation, the manner in which they are 

 folded and spread out may be seen : (see figure 252, which 

 exhibits the muscular fibres, &c.) This sketch I made from 

 an animalcule, which, at short intervals, repeated the 

 operation of folding and unfolding these organs without 

 altering its situation, thus affording me a good opportu- 

 nity to view it. Near the wheels on the inferior side of 

 the body is the sexual organ, as shewn in figure 251 ; 

 and below this, the heart-shaped body, or bulbous oeso- 

 phagus, which, from its lateral motion and the trans- 



