250 



The Field Naturalist's Qttartcrly August 



Fig. 8. — Actinophrys. 



incidentally mention that the animals which build the beautiful little 

 marine shells familiar to microscopists as Foraminifera and Polycystina 



(Radiolaria) are identical in structure with 

 Actinophrys. So far all the forms described 

 belong to the Rhizopoda and have no 

 definite cell-wall. 



The forms comprised in the other large 



division of Protozoa — the Infusoria proper 



— all have a definite cell-wall. Amongst 



the many hundreds of species it is very 



difficult to select types for description, but 



I will take first one of the most beautiful 



and abundant, namely, Vorticella, which 



may be found in myriads attached to the 



weeds in ponds and canals. In autumn 



when the weeds have ceased to grow I have often seen them so coated 



with Vorticella that there was a greyish film over the plants distinctly 



visible to the naked eye. 



If a piece of this weed be placed under the microscope (using a com- 

 pressorium and black background illumination), a scene of wondrous 

 beauty and animation is presented to view. Attached to the weed are 

 hundreds of living crystal vases, their edges fringed with circles of 

 whirling hairs which flash in the brilliant light as they lash the water 

 into circling eddies. Suddenly the edge of a vase caves in and the 

 creature is withdrawn as if by magic, its stem thrown into a close spiral 

 coil, which shortens it to a fraction of its full length. The next moment 

 the stem slowly and gracefully uncoils, the edges of the vase unfold, 

 and the cilia again resume their mad course. 



Not to dwell longer on the charming grace of this spectacle, we will 

 proceed to examine an individual Vorticella, and notice first the points 

 in which it resembles Amoeba. The interior of the body is filled with 

 a granular protoplasm, in which we notice food vacuoles, a contractile 

 vesicle, and a nucleus. This last in Vorticella is a long sinuous band 

 (Fig. 9). On further examination we shall find many points in which 

 Vorticella is more highly specialised than Amoeba. It has a distinct 

 cell- wall, which is cup-shaped, and this cell-wall has appendages. The 

 most important is the stem which unites the animal to the weed, and 

 which contains a muscle that by its contraction throws the stem into 

 spiral folds. Vorticella cannot take food in anywhere, like Amwba, but 

 has a distinct mouth just within the rim of the cup : a short tube or 

 oesophagus leads directly into the interior protoplasm. Lastly, Vorti- 

 cella is provided round the edge of the cup (which is thickened like a 

 pneumatic tyre) with a quantity of fine lashes called cilia ( = eyelashes), 

 which, by their motion, create currents in the water. The name 

 Vorticella means a little whirlpool. Particles of food brought by the 

 current are selected by the animal and taken into the mouth, where they 

 are held till they accumulate into a tiny pill ; then they are swallowed. 

 The animal certainly exhibits sensibility in differentiating between various 



