BDELLOID ROTIFERA OF SOUTH AFRICA. 51 



the body width, and the tips form the corners of a figure, almost 

 a square. The convex bend of each sickle is outside, and the 

 inner concaves face each other diagonally. The spur is of ellip- 

 tical form, and is motile at the base, at least it can be bent down- 

 wards. 



The rostrum is of the usual Philodine type, and is short and 

 stout. It has a double frontlet, and bears long cilia, which are 

 more powerful than those of the corona. It is capable of taking 

 an extremely firm hold. When the animal is feeding, the rostrum 

 is not tossed over. 



The corona might be looked on as decadent, with the whole — 

 wheels and pedicels — reduced to thin discs ; or — what is much 

 more probable — as rudimentary, and advanced half-way in the 

 evolution of a corona of the Philodina-tyi^e, from a prone face of 

 the Diglena-type. 



On the ventral face of the post-rostral segment, is seen a double 

 rotulate arrangement, somewhat like two thin discs inset in the 

 surface, and barely rising above it. These project very slightly, 

 right and left, over the segment, and probably bend slightly 

 towards each other. There is a narrow space or alley between. 

 Along the rims of these discs, cilia are borne up the centre and 

 round towards the posterior, where the discs are not well defined 

 and the cilia are not visible. Just here — at the back of the 

 wheels — the body depth increases in the ventral direction, and, 

 projecting almost over the posterior of the discs, prevents a clear 

 view of the back of them. This high boundary determines the 

 oral entrance, into which the alley between the discs leads. This 

 alley, down which the current streams, would thus be analogous 

 to the sulcus in Philodina. 



The gullet is extremely short, as the jaws come almost to the 

 orifice, but do not project. There is a short oesophagus, similar 

 to that seen in some species of Ploima between the mast ax and 

 the stomach. 



M. falcatus is closely plicate, and many samples are so wrinkled 

 and reticulated that the optical difficulties are increased to such 

 an extent as to make it almost impossible to see the internal 

 parts. These wrinkled specimens are usually seen after the 

 water has been kept for a day or so. Seldom are live specimens 

 found after the second day in the bottles, even when the water 

 has been aerated periodically. This, taken with the fact that 



