4 Transactions of the Society. 



The ciliary wreath is a continuous ring round the outside of 

 the corona, inside which there is a variable arrangement of stiff 

 setse. 



The bunch of setse on the foot, which is one of the marks of 

 this genus, consists of four or five stiff hairs pointing back in a 

 divergent pencil, just over the base of the toes. 



The gastric glands vary but little in shape and size, being 

 usually rather large irregular sacs. In D. caeca they are generally 

 pigmented red ; in tenuior sometimes pigmented brown ; in lacinu- 

 lata sometimes pigmented pink. We have never observed any- 

 thing approaching this in the other species. 



The lateral canals are normal, each canal carrying five vibratile 

 tags. 



i The construction of the jaws of this genus is exceedingly 

 difficult to elucidate either by drawings or description. They 

 consist of the usual parts, but these are attached to plates. By a 

 special arrangement of the muscles which work the unci and rami, 

 it is able suddenly to expand the cavity enclosed within these plates, 

 thus sucking in its food. This suction is its method of securing 

 its food ; not, as Gosse suggests, a protruding and prehensile action 

 of the jaws. His drawings in Manduc. org. in Class Rotif. Phil. 

 Trans. Roy. Soc. pp. 432, 433, pi. 17, figs. 32-37 (lacinidata and 

 gibba), are much more accurate than his description. 



Take, for example, either D. eva or D. vciitripes. The food of 

 these two species is chiefly diatoms. These they secure simply by 

 the suction caused by the rapid expansion of the mastax cavity 

 and the rush of outside matter to fill the vacuum. We have 

 many a time observed a whole hard diatom almost one-third as 

 large as the trunk of the animal sucked in, and without any 

 mastication, pass straight on through the oesophagus right to the 

 stomach, there to be acted upon by the gastric fluids alone. 



All the other species feed on spores or flocculent matter, which 

 are sucked in in a similar manner without any attempt at masti- 

 cation. In fact the jaws of this genus are not used for mastica- 

 tion. 



In giving the sizes of the different species, the maximum size 

 observed by us is taken, and in those cases where the immature 

 specimens fall much short of this standard special note is made of 

 that fact. The words " total length " are used to describe the 

 measure taken from the most projecting point of the head to the 

 tip of the toes when carried straight behind. The " breadth " is 

 the width at the widest part of the animal from a dorsal view. 

 The " height " or " depth " signifies the maximum transverse sec- 

 tion or elevation from a lateral view. All these measurements 

 vary in every species ; but the proportions between them are 

 fairly constant. 



All the figures of the plates (except 2 and 85) have been 



