438 



BOTIFEEA. 



Fig. 227. 



exhibited on a still larger scale in fig. 228. This curious masticating 

 instrument consists of three distinct pieces, or teeth, which are made to 

 work upon each other by the contractions of the gizzard, so as to tear 

 in pieces or bruise all matters 

 made to pass through the cavity 

 containing them. The central 

 piece (fig.225,/) maybe compared 

 to an anvil, presenting on its upper 

 surface two flattened facets ; and 

 upon these the other two teeth 

 (that might, without much stretch 

 of fancy, be compared to two ham- 

 mers) act. Each of the superior 

 teeth may be described as con- 

 sisting of two portions united at 

 an angle : the larger portion, or 

 handle as it might be called, serves 

 for the attachment of muscles ; 

 whilst the other part is free in the 

 cavity of the gizzard, and works 

 upon the facets of the anvil, the 

 edge being apparently divided into 

 teeth resembling those of a comb, 

 and evidently adapted to bruise or 

 tear substances submitted to their 

 action. Such is the transparency 

 of the whole animal, that the effect 

 of these remarkable organs upon 

 the animalcules used as food is distinctly visible under a good micro- 

 scope ; and if the Rotifer be compressed between two pieces of glass, so 

 as to break down the soft textures of its body, the teeth may, from their 

 hardness, be procured in a detached state for minute examination. The 

 whole apparatus described above evidently resembles very closely the 

 kind of stomach met with in the Crustacea, to which the Rotifera will 

 be found gradually to approximate. 



(1134.) In Melicerta ringens&Q alimentary canal commences with a 

 small oval orifice situated near the sinuated disk formed by the rotatory 

 organs. It opens into an oesophagus that conducts the food down to 

 the gastric teeth (fig. 227, 1, e). These, according to Professor William- 

 son's very excellent memoir upon the subject*, are implanted in a large 

 conglobate cellular mass, which completely invests them. Their appear- 

 ance, when highly magnified, is accurately represented in fig. 228; they 

 consist of two essential portions a pair of strong crushing plates, which 

 bruise the food, and various appendages affording leverage and facili- 

 * Quarterly Journal of Microscopical Science, vol. i. p. 1. 



Melicerta ringens (after Prof. Williamson) : 

 a a, ciliated lobes, constituting the rotatory 

 apparatus; b, hooks, called by Schaffer "the 

 lips;" c, rotatory flap, or "pellet-cup" 

 (Gosse) ; d d, tentacular organs ; e, gizzard, con- 

 taining the gastric teeth ; f, upper stomachal 

 cavity ; g, inferior stomachal cavity ; h, anal 

 outlet ; i, protuberance occasioned by the act 

 of defecation ; k, ovary ; I, dilated oviduct ; 

 TO, filamentary spermatic tube (?) ; n n, mus- 

 cles of caudal appendage ; o, prehensile organ ; 

 p p, corpuscles floating in the perivisceral 

 fluid ; q q, ova nearly ready for expulsion. 



