414 GENEEAL HISTOBT OF THE INFUSORIA. 



itself single or multiple, which is the jaw properly so called. In most cases, 

 says Siebold, the homy jaws consist of two bent, geniculate processes, an 

 anterior and a posterior ; the latter gives attachment to the muscles moving 

 the apparatus, whilst one or several teeth are developed on the former. In 

 some many- toothed Rotatoria, each jaw is provided with three homy arches 

 {e. g. in Philodina, Lacinularia, and Melicerta). Two of these arches (arcus 

 superior et inferior) are turned inwards, whilst the third (arcus exterior) is 

 directed outwards. To the under arch the muscles of the jaw are attached, 

 which move the other two arches, with their transverse teeth, against each 

 other. 



"Williamson gives the following particular account of the grinding apparatus 

 of Melicerta : — " The gastric teeth consist of two essential portions, a pair of 

 strong crushing plates, which braise the food, and various appendages afford- 

 ing leverage and facilitating the action of the muscles upon them. The 

 crushers are two broad elongated plates (XXXYII. 26), each being about 

 ■g-i-g-th of an inch long, and separated from each other at the mesial line, near 

 which they become much thickened. From each of these plates there proceed 

 laterally numerous parallel bars, all of which are somewhat thickened at their 

 inner extremities where they are attached to the plates, whilst at their oppo- 

 site ends they are united mth the others of the same side by a curved con- 

 necting bar (fig. 26), from the outer sides of which are given oif various 

 loops and processes. The three uppermost of these bars are the largest, the 

 rest gradually diminishing in size and strength as we descend, the inferior 

 ones being almost invisible. Prom the upper extremities of the two crushers 

 there project upwards and backwards two slender prolongations imited by a 

 kind of double hinge-joint near their apex, where they not only play upon 

 each other, but also on a third small central fixed point, lodged in a little 

 conglobate cellular mass. Ehrenberg only describes three transverse bars 

 on each side, which he regards as teeth. It is obvious that he has only 

 noticed the thi^ee upper and larger pairs. It is equally evident that these 

 transverse teeth, as he terms them, do not move upon the strong longitudinal 

 plates, as he imagines, but are firmly united with them. Muscles are either 

 attached to the divergent peripheral processes, or to the cellular mass in 

 which these processes are imbedded, causing the entire apparatus to separate 

 into two parts along the mesial line by means of the hinge joint, the so- 

 called teeth merely transmitting the motor force to the two longitudinal 

 plates. These latter appendages are thus made to play upon each other with 

 great power, and act as efficient crushers, bruising the food before it passes 

 into the stomach, as is the case with the gastric teeth of the Crustacea. 

 From the above remarks it will be seen that, though in its construction the 

 dental apparatus is more complex than is represented by Ehrenberg, in its 

 mode of working it is less so." 



Prof. Huxley, to quote another accurate English observer, has seen in 

 Lacinularia sociaJis, as also in Stephanoceros, the " pharyngeal armatui'e com- 

 posed of four separate pieces (XXXYII. 30) : two of these (which form the 

 * incus ' of Mr. Gosse) are elongated triangular prisms, applied together by 

 their flat inner faces ; the upper faces are rather concave, while the other 

 faces are convex, and upon these the two other pieces (the mallei of Mr. 

 Gosse) are articulated. These last are elongated, concave internally, convex 

 extemally, and present two clear spaces in their interior ; fi'om their inner 

 surface a thin curved plate projects inwards. At its anterior extremity this 

 plate is brownish, and divided into five or six hard teeth with slightly en- 

 larged extremities. Posteriorly the divisions become less and less distinct, 

 and the plate takes quite the appearance of the rest of the piece." This is 



