BDELLOID ROTIFERA OF SOUTH AFRICA. 55 



round the shoulders aud backwards, and one from behind and 

 under. I have seen what I took to be a muscle attached to the 

 bottom mass and branching upwards into two which are fixed, 

 one each, to the posterior ends of the rami. When the jaws 

 begin to act, the first motion is usually a downward one in the 

 centre. This would be caused by the pulling of the branching 

 muscle referred to. As the pulling is continued, the chisel-faced 

 teeth are ground against each other and downwards, and throw 

 up the mallei. Then the muscles from the shoulder muscular 

 masses act, and pull the mallei down ; the chisel-faced teeth 

 oppose each other at their lowest points, and th^ow the inside 

 faces of the jaws (rami) up and away from each other with a slight 

 rotation, as the front ends of the jaws are muscularly connected 

 while the posterior ends are free. The jaws separate so far in 

 P. grandis that when open the chisel-faced teeth can be seen 

 between them from above. In each up-and-down motion the 

 shock can be observed, just when the full pressure comes to bear 

 on the opposing chisel faces. The resulting slight rock on the 

 point of pressure can be seen. 



The position of Monoceros falcatus seems to be somewhere 

 between Ploima and Philodina. There are features which seem 

 to show that it might very well have been evolved from free- 

 swimming ancestors among the Ploima. The jaws, corona and 

 spur might have come from some tailed form of Pleurotrocha. 

 Probably there were parallel roads attempted from Ploima to 

 Philodina. M. falcatus on one of these failed to get all the way, 

 and Microdina paradoxa also failed on another road. 



One is tempted, at this stage, to look for signs, among the 

 Bdelloida, of any links towards other branches of the Eotifera. 

 There are the horn-like processes of the corona of Ceratotrocha 

 cornigera, which might point the way to the Floscularia, possibly 

 the farthest advanced of the Eotifera, as one of them, F. moseli 

 (5), has rudimentary kidneys and is thus probably the highest 

 of all. 



Habitat. — Not far from Algoa Bay, to the west along the coast, 

 are the grass-covered Cape flats. Walking across these flats 

 uear the farm of Draaifontein, one suddenly comes on a narrow, 

 deep ravine, whose existence was quite unsuggested by the flat 

 surroundings. On descending to the bottom, through the scrub 

 and treeg, b, little stream is found, whose bankg a,re covered 



