72 N. E. GREEN ON CILIARY ACTION IN ROTIFERA. 



abundant in the floscule, but each animalcule of the wheel-bearing 

 class possesses them more or less. In the common rotifer they 

 terminate the process which extends from the head when the 

 wheels are withdrawn, and may be seen in frequent vibratory 

 action, as though testing the condition of the water, while the body 

 of the creature is moved here and there in search of food. When 

 their report is encouraging, out come those wonderful appendages 

 and work as usual ; but should the result not equal the expecta- 

 tion, they are withdrawn, and the informers again employed. We 

 have observed this action particularly in those individuals which 

 had been kept for some time in a limited supply of water. 



In Vorticella, Brachionus, Philodina, and especially in Melicerta 

 Floscularia, and Stephanoceros these hairs may be observed, and in 

 each case their duty seems to be somewhat the same. Those ac- 

 customed to watch the movements of Vorticella may have observed 

 the manner in which that beautiful anterior fringe of cilia, which 

 assists in the formation of the vortex, is sometimes thrown 

 forward, straight and motionless, though but for a moment ; but if 

 its answer is not satisfactory, another jerk is given, and a fresh 

 examination made before the rotatory movement is set up. Again, 

 in Melicerta, how many weary moments have we spent in watching 

 those tufts of short cilia, which just peep over the edge of the case 

 when the animal is retracted, and are evidently designed to convey 

 information of any change in the surrounding medium — this may 

 be tested by allowing a few drops of fresh water to pass over the 

 end of the case, for soon the influence is felt, and the creature 

 comes slowly out to realise the benefit of the change. But with- 

 out some explanation of this kind, it seems difficult to assign a 

 duty to those infinitely delicate threads which radiate from the 

 head of the floscule — these would be little better than unnecessary 

 excrescences if some useful work is not performed by them. 



With regard to the wheels, we will first make a few observa- 

 tions on the direction of the movements of cilia, by which the illu- 

 sion of rotation is produced, and then speak of the duplicate 

 character of the organ itself; and if in these remarks we simply 

 repeat the statements of others, even this repetition is not destitute 

 of value, for on a subject of such intricacy, every independent testi- 

 mony is acceptable. We have watched both earnestly and long to 

 discover the nature of these rotatory illusions, and not until the 

 anhnalculae had been kept in the same limited supply of water, and 



