472 INTERNAL STRUCTURE OF ROTIFERA. 



wheels is a prominence bearing two red spots (b), supposed to be 

 rudimentary eyes, and having the mouth (a) at its extremity ; this 

 prominence may be considered, therefore, as a true head, notwith- 

 standing that it is not clearly distinguishable from the body. This 

 head also bears upon its under surface a projecting tubular organ (d), 

 which was thought by Professor Ehrenberg to be a siphou for 

 the admission of water to the cavity of the body for the purpose 

 of respiration ; this, however, is certainly not the case, the tube 

 being imperforate at its extremity ; and there seems much more 

 probability in the idea of Dujardin, that it represents the antennae 

 or palpi of higher Articulata, the single organ being replaced in 

 many Rotifera by a pair, of which each is furnished at its ex- 

 tremity with a brush-like tuft of hairs that can be retracted into 

 the tube. The oesophagus, which is narrow in the Rotifer, but is 

 dilated into a crop in Stephanoceros (Fig. 246) and in some other 

 genera, leads to the masticating apparatus (Fig. 244, e), which in 

 these animals is placed far behind the mouth, and in close proxi- 

 mity to the stomach. 



357. The Masticating apparatus has recently been made the 

 subject of attentive study by Mr. P. H. Gosse ; who has given an 

 elaborate account of the various types of form which it presents 

 in the several subdivisions of the group.* The following descrip- 

 tion of one of the more complicated will serve our present pur- 

 pose. The various movable parts are included in a muscular bulb, 

 termed the mastax (Fig. 245 a), which intervenes between the 

 buccal funnel (m) and oesophagus (p). The mastax includes a pair 

 of organs, which, from the resemblance of their action to that of 

 hammers working on an anvil, may be called mallei, and a third, 

 still more complex, termed the incus. Each Malleus consists of 

 two principal parts placed nearly at right angles to each other, the 

 manubrium (c), and the uncus (e) ; these are articulated to one 

 another by a sort of hinge-joint. The former, as its name imports, 

 serves the purpose in some degree of a handle ; and it is the latter 

 which is the instrument for crushing and dividing the food. This 

 is done by means of the finger Jike processes with which it is fur- 

 nished at the edge where it meets its fellow ; these being five or 

 six in number, set parallel to each other like the teeth of a comb. 

 The Incus also consists of distinct articulated portions, namely, 

 two stout rami (a) resting on what seems a slender footstalk (h) 

 termed the fulcrum ; when viewed laterally, however, the fulcrum 

 is seen to be a thin plate, having the rami so jointed to one edge 

 of it that they can open and close like a pair of shears. The 

 uncus of each Malleus falls into the concavity of its respective 

 ramus, and is connected with it by a stout triangular muscle (£) 

 which is seen passing from the hollow of the ramus to the under 

 surface of the uncus. It is difficult to say with certainty what is 



• "Philosophical Transactions," 1856, p. 419. 



