AN ANATOMICAL PUZZLE. 23 



tary canal of a wonderfully complex character. The wheel-like 

 organs from which the class takes its name are most character- 

 istically seen in the Common Rotifer (Botifera vulgaris), and 

 in this case consist of two disc-like lobes at the upper extremity 

 of the body, the margins of which are fringed with long cilia, 

 the organs specially concerned in the apparently rotatory move- 

 ment. 



The singular appearance produced by the continued play of 

 the Rotifer's cilia was for a long time a subject of inexplicable 

 mystery to microscopical observers. It was as opposed to all 

 known movements of organic structures as if a man's head should 

 spin round incessantly on the top of his neck ; and yet there 

 seemed to be no possibility of doubting that the two circular 

 organs of the animalcule did thus revolve. After long and careful 

 observation, the source of the illusion became apparent. The sup- 

 posed wheels were found to be mere circlets of delicate cilia, which 

 bending and unbending in rapid succession, like a field of corn on 

 a windy day, gave rise to that wheel-like rotation which had 

 proved such a fruitful source of perplexity and doubt. 



The Common Rotifer and its nearest allies swim freely 

 through the water, rowed along with considerable rapidity by 

 means of their ciliated lobes. They have the power, however, of at- 

 taching themselves at pleasure, and at the lower extremity of the 

 body they are provided, for this purpose, either with a cup-like 

 sucker, or with a pair of minute forceps, by means of which they 

 seize hold of the stems and leaves of aquatic plants, and rest for 

 a time from theii more active exertions. But, fixed or free, it 

 matters little to the Rotifer, for he has but to set those paddle- 

 wheels of his in motion to produce a vortex in the water, which 

 brings him food in abundance ; and yoii can rarely light upon 

 one whose cilia have been long at work in capturing, or rather 

 collecting, prey, without finding that its masticatory apparatus 

 also is busily employed tearing and pounding away at the mass 

 of food with which its exertions have been rewarded. 



Many of the Rotifera are fixed to one spot throughout the en- 

 tire period of their lives, and amongst these sessile forms are to bo 

 found by far the most beautiful species which the race includes. 

 One of the most elegant of these is the Stephanoceros Eichornii, 

 which inhabits a delicate gelatinous tube, like the straight 

 glasses used by the confectioners, to the bottom of which it is 



