122 



C. F, ROUSSELET ON DIPLOIS TRIGONA. 



The integument is smooth, soft, and flexible, but yet possesses a 

 certain stiffness, so that a number of folds behind and along the 

 sides of the body remain constant. In contraction the body is a 

 perfect ball, but the foot is not retractile. The corona is as broad 

 as the body, oblique, and consists, as in M. orbiculodiscus, of two 

 concentric bands of cilia (Fig lb) ; the outer wreath bends 

 inwards on the frontal side, and seems to be continuous with the 

 smaller inner wreath which surrounds the mouth. The middle 

 part of the trochal disc rises into two elongated fleshy prominences, 

 and between these the mouth is situated at the bottom of a funnel- 

 shaped depression, clothed with very fine and dense cilia. When 

 treated with a little cocaine-spirit mixture many Rotifers often swim 

 for a long time with their heads closely pressed against the cover 

 glass of the compressor, and in this way I obtained very good 

 views of the front of the head, which is otherwise difficult to see. 

 There is a gap in the frontal part of the ciliary wreath, and just 

 there are two style-like seta3 which do not vibrate. The brain is a 

 large, rounded, clear cellular mass, carrying a crimson eye with a 

 minute crystalline sphere on the under side ; the sphere is turned 

 towards the brain, so that all rays of light reaching it must pass 

 through part of the transparent brain. The dorsal antenna pro- 

 trudes from a well-marked prominence above the brain, and the 

 lateral antenna? are readily seen in the usual position in a little 

 fold of the skin in the lumbar region. The mastax is large, and 

 the jaws of peculiar form, as will best be seen by the drawing (Fig. 

 Id and le). One maleus only has been drawn, but, of course, 

 there are two of the same shape. A short, narrow oesophagus leads 

 to a wide stomach and intestine, the former carrying the usual 

 gastric glands. The stomach has thick walls, and the cells are 

 mostly granular, which gives it a dark appearance. The contractile 

 vesicle is large ; the lateral canals, ovary, longitudinal, and trans- 

 verse muscular bands are as usual in allied species. The foot is 

 stout, three-jointed, ending in a single toe. With a high power, I 

 was, however, able to see a line dividing the toe longitudinally in a 

 larger ventral and smaller dorsal portion, as if there were present 

 a small vanishing spur, closely appressed to the toe (Fig. lc). 

 Two foot-glands are present. 



When swimming in the open water this Rotifer has usually an 

 upright position and moves forward in frequent little jerks. The 

 movements and mode of swimming are very constant in Rotifers, 



