On (Ecistes Janus, &c. By C. T. Hudson. 3 



members of this genus, the disk is in many places very thin and 

 transparent, while across it run stout thickenings. Fig. 5, between 

 which the thinner portions are folded when the disk is closed, and 

 which serve both to open the disk and to keep it extended in 

 various degrees — acting indeed somewhat like the ribs of an 

 umbrella. These stout ribs protrude in a squarish bundle when 

 the creature begins to open its disk, and give the head a most 

 characteristic outline, which I have drawn in the case of CE. 

 umbella in this Journal, vol. ii. (1879), p. 1. The contrast 

 between the thinner and thicker portions of the disk is well seen 

 in a side view, as in Fig. 3, especially with dark field illumination, 

 under which the ribs, p, jp, stand out distinctly, while the sub- 

 stance of the disk between becomes nearly invisible, its edge being 

 marked out by the two parallel curves of cilia. 



(E. Janus is a large rotifer, and the ciha of its trochal disk are 

 unusually fine, while the groove that lies between the primary and 

 secondary rows of cilia, is both broad and deep. Should the 

 motion of the larger cilia be checked by contact with the side of 

 the cell in which it has been placed, they may be easily counted, 

 while their whip-like mode of action becomes plainly visible. 

 Even in the case of the finer secondary row, individual cilia may 

 be occasionally seen, while the combined efiect of the whole does 

 not admit of question. As in all the Melicertidse, the action of the 

 larger cilia draws a current of water at right angles to the trochal 

 disk, and atoms floating in the current impinge on the disk, slide 

 over its surface, and then slip over the edge between the bases of 

 the larger cilia into the groove between the two rows, along which 

 they are driven by the smaller cilia to the mouth. Above the 

 mouth the groove ends in two ciliated knobs, which are constantly 

 approaching to or receding from each other as they regulate the 

 supply ; and beneath them again, but above the mastax, a pair of 

 lips, if I may use the term, are often seen to spring up to seize or 

 reject some morsel. The greater part of the current from the 

 groove passes beyond the mouth along a ciliated trough, ending in 

 what Mr. Gosse terms the " chin." In (E. Janus this " chin," 

 Fig. 6, is peculiar in shape, being divided into two peaks. Below the 

 divided chin is a pair of thin walls, looking exactly like the supports 

 of a bracket — the chin being the bracket itself. The chin above, 

 the walls on each side, and the concave surface of the body which 

 they enclose, together make something very like Melicerta's ciliated 

 cup ; but I have not been able to detect any cilia, while in (E. 

 ^ilula there is a distinct ciliated tract lying beneath the chin. 

 Below this cup-like spot is a knob, Figs. 2, 3, which is rather more, 

 prominent than in some of the tube-makers, and just above I could 

 now and then see two or more curved bristles which are peculiar 

 to (E. Janus. 



B 2 



