THE EOTIFEKA. 267 



each aperture stretches forth a neck ornamented with concentric 

 rings of golden hair, and terminating in a head embellished 

 with a tiara of delicately feathered, rainbow-tinted tentacula. 

 The whole looks like a garden-bed enamelled with gay flowers 

 of elegant form and variegated colours. 



If size alone were a criterion of classification, the Eotifera 

 would have to be ranked among the microscopic Protozoa, as 

 they are scarcely visible to the naked eye ; but a more com- 

 plicated organisation separates them widely from these lowest 

 members of the animal kingdom, and entitles them to be 

 placed next to the worms. 



Ptygura melicerta. — (A rotifer highly magnified.) 



1. Partially expanded. 



2. Completely expanded, the cilia in action causing currents indicated by the arrows. 



3. Contracted. a. Contractile vesicle. b. Situation of the anal orifice. 



They are chiefly characterised by a remarkable rotatory 

 or ciliary apparatus, whose vibrating motions, whirling the 

 water about in swift circles or eddies, engulf in a fatal vortex 

 their microscopic food, or enable them to swim from place to 

 place. Such is the crystal transparency of these curious 

 little creatures that their internal structure can be easily 

 recognised. The mouth is placed immediately below the rota- 

 tory apparatus, and when once an unfortunate animalcule has 



