Recent Researches on the Infusoria, 'S06 



p, ,. VI. Of the Dental System of the Rotatoria. 



The discovery of the teeth in the infusoria, affords a striking 

 proof that the smallest organized beings are not necessarily also 

 the most simple in structure. This truth becomes still more 

 manifest when we learn that these organs exist under several 

 forms, which are so constant and regular, that the infusoria 

 might almost, like quadrupeds, be arranged according to their 

 teeth. However, in giving a systematic view of the principal 

 varieties in the form and structure of the teeth, Dr Ehrenberg 

 does not propose to found on it a system of arrangement, to 

 which he admits there would be serious practical objections. 



The pharynx of the Rotatoria is surrounded by four hemi- 

 spherical muscular masses, placed opposite one another like the 

 limbs of a cross, which become very obvious when in motion. 

 Two of these are armed with the maxillae and teeth, which be- 

 ing formed of a hard substance, may be disengaged from the 

 soft parts, and rendered distinctly visible, by crushing the 

 animal between two plates of glass. In the greater number of 

 Rotatoria, each maxilla consists of an anterior and a posterior 

 portion or process, which are joined together at an angle (Fig. 

 17, 19). The posterior process is sunk in the muscular sub- 

 stance, and thus fixed, the anterior is directed towards the 

 opposite maxilla, and at its free extremity bears one or more 

 teeth. 



In a smaller number of genera the structure is somewhat dif- 

 ferent. Each maxilla is shaped like a stirrup or like a bow with 

 a double string, and the teeth are laid across it in the same po- 

 sition as arrows across a bow, being fixed at both ends (Fig. 21, 

 23). The bow is directed outwards and placed horizontally ; the 

 pieces representing the strings are situated inwardly next to thie 

 opposite maxilla ; they are not straight, but form two arches 

 cotinected by their extremities, and placed in the same vertical 

 plane. The lower arch gives insertion to the muscles, the up- 

 per one supports the teeth, which are fixed to it at their in- 

 ner extremity, the outer resting on the bow. 



According to these two principal forms of the teeth and jaws, 

 the Rotatoria might be divided into two groups, distinguished 



VoiL. XV. NO. XXX,— OCTOBER 18S3. U 



