VIII GIZZARD 211 



asymmetrical. In the " submalleate " type (B) the mallei only 

 are slender ; in the " forcipate " type (D) both the unci and 

 rami are slender and sharply pointed. 1 In the " malleoramate " 

 type (E) the manubrium is a curious looped structure, while the 

 uncus is formed of a number of parallel slender elongated teeth ; 

 this characterises the family Melicertidae, and the genera Triar- 

 thra, Pterodina, and Pedalion. In the " uncinate " type (G) the 

 mallei are simply incurved hooks with a few teeth at the free 

 end, the rami are simple or absent, and there is no fulcrum ; this 

 type occurs in Flosculariaceae only. In Asplanchnidae the rami 

 are large and hooked, constituting the " incudate " mastax (F) ; 

 but here reduced mallei are often present, and in Asplanchnopus 

 they are almost as well developed as in Melicertidae, affording a 

 transition to the malleoramate type. In this group too the 

 mastax has a very peculiar form ; it is divided into two cham- 

 bers, dorsal and ventral. The dorsal chamber forms a great 

 purse-like sac or crop, with a framework of four longitudinal bars : 

 into this the gullet and pharynx open. The ventral pouch is 

 much smaller, and in its base the large rami are inserted, so 

 that they can be protruded into the crop. This ventral sac 

 with the rami may even be everted through the crop and the 

 mouth, to swallow the small Eotifers and Entomostraca which 

 form the food of this group, or to eject the undigested remains 

 of the food. Two lateral sacs open at the junction of the ventral 

 pouch and the crop, but whether they play a part in the deglu- 

 tition of food or in the disgorging of faeces is uncertain. The 

 fact that the whole of this apparatus is lined by a non-ciliated 

 chitinous cuticle justifies our view that it is simply an enlarge- 

 ment and specialisation of the mastax. 



The tropin in Bdelloids also are only represented by the 

 rami, which have the form of segments of a sphere, excavated 

 on the curved sides for the attachment of muscles, and trans- 

 versely ridged on the two flat sides ; the gizzard is here called 

 " ramate " (H). 



It will be seen that the characters of the gizzard are very 

 useful for classification, only breaking down indeed in the 



1 A modification of this type is seen in the parasite Drilophagus, where the unci 

 and rami are two-pronged at the end, but the tropin are not movable on one 

 another, but protrusible as a whole to serve as an organ of attachment to the 

 Oligochaete Lumbriculus, to which this Rotifer attaches itself. See Vejdovsky, 

 "Ueb. Drilophaga bucephalus," etc., in SB. Bohm. Ges. Jahrg. 1882 (1883), p. 390. 



