ROTATOR!^. 341 



appearance is not unlike that of a flower of four unequal 

 petals ; from which circumstance Linnaeus gave it the 

 name ringens, by which it is still known." 



Below the large petals on the ventral aspect, and just 

 above the level of the projecting respiratory tubes, is a 

 small circular disc or aperture, within the margin of which 

 a rapid rotation goes on. This little organ, which seems 

 to have hitherto escaped observation, Mr. Gosse can com- 

 pare to nothing so well as to one of those little circular 

 ventilators which we sometimes see in one of the upper 

 panes of a kitchen- window, running round and round, for 

 the cure of smoky chimneys. The gizzard, or muscular 

 bulb of the gullet, is always very distinct, and its structure 

 is readily demonstrated. It consists of two sub-hemisphe- 

 rical portions, or jaws, each of which is crossed by three 

 developed teeth, which are succeeded by three or four 

 parallel lines, as if new teeth might grow from thence. 

 The teeth are straight, slender, swelling towards their 

 extremity, and pointed. These armed hemispheres work 

 on each other, and on a Y-shaped or tabuliform apparatus 

 beneath, common to most of the Rotifers, but in this genus 

 very small. 



The pellets composing the case are very regular in form 

 and position : in a fine specimen, about the 1-2 8th of an 

 inch in length when fully expanded, of which the tube was 

 the 1-3 6th of an inch, Mr. Gosse counted about fifteen 

 longitudinal rows of pellets at one view, which might 

 give about thirty-two or thirty- four rows in all. 



In November, 18'50, Mr. Gosse found a fine specimen 

 attached to a submerged moss from a pond at Hackney; 

 this he saw engaged in building its case, and at the same 

 time discovered the use of the curious little rotatory organ 

 on the neck. When fully expanded, the head is bent back 

 at nearly a right angle to the body, so that the disc is 

 placed nearly perpendicularly, instead of horizontally ; the 

 larger petals, which are the frontal ones, being above the 

 smaller pair. Now, below the large petals (that is, on the 

 ventral side) there is a projecting angular chin, which is 

 ciliated ; and immediately below this is the little organ in 

 question. It appears to form a small hemispherical cup, 

 and is capable of some degree of projection, as if on a short 



