THE ROTIFERA. 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 Rotifera 
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 m action causing currents inaicated by the arrows. 
3. Contracted. a. Coutractile vesicle, 6. 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 
