86 THE VORTICELLIDE. 
(3) Epistylis leucoa, [Plate I., Fig. 6.] Stalk shorter, rigid, not 
coutractile, branching irregularly at the top, so as to form a 
large head of bells. 
(4) Zoothamnium arbuscula. Stalk thick, tapering, contractile, and 
branched horizontally at the top, each branch subdividing in 
the same plane. Bells of two kinds on both sides of branches.* 
(1.) Vorticella nebulifera. The name Vorticella, diminutive of 
the Latin vortex, a whirlpool, was given to the genus in allusion 
to the currents which they produce in the water, and this species 
was called nebulifera, cloud bearing, because, from its gregarious 
habits, it imparts a cloudy appearance to the objects to which it is 
attached, In its normal condition [Plate I., Fig. 1] the Vorticella 
is a little bell supported on a long, slender, hollow stalk, which con- 
tains a well developed muscle, easily seen with an obliquelight. Although 
no nerves have been detected in connection with it, its powers of sensi- 
bility and contractility are very great. When expanded the tube is 
straight, but the enclosed muscle is always spiral, and when contracted 
the tube is also thrown into a spiral, [Fig. 2,] and thus shortened. The 
act of contraction is very sudden, but the re-expansion much slower. 
During contraction the ciliary wreath is withdrawn into the body. As it 
slowly uncoils, first the stem straightens, then the centre of the bell rises 
up, and the edges curl over outwards, and, lastly, the cilia are set in 
motion. Of course the converse of this takes place when the animal 
contracts, but then the action is so swift that the eye cannot follow it. 
The body consists of (1)an outer layer, the cuticle, marked with fine, 
dense, parallel strie [Figs. 1 and 2;] (2) an inner cortical layer, in which 
are imbedded a contractile vesicle [Fig. la] and a nucleus, [Fig. 1e,] the 
latter usually invisible unlessreagents are employed to show it; and (3) an 
interior mass of sarcode, containing several globular bodies called food- 
vacuoles. At the top margin of the bell there is a projecting rim 
[Fig. 1c] surrounding a circular space called the disc, [Fig. 1b,] at one 
end of which is a depression called the vestibule, [Fig. 1d,] and at the 
bottom of this the mouth and anus are situated, the latter, however, only 
visible when in use. There is a short esophagus leading from the mouth 
into the interior. The rim is plentifully supplied with cilia, which, by 
their constant action on the surrounding water, sweep a succession of 
minute particles of food into the vestibule, where they accumulate into 
a kind of pellet. When sufficient is collected the animal gulps it down, 
together with a small portion of water, and this mouthful floating into 
the sarcodous interior becomes a food-vacuole. 
It is in the processes of multiplication and reproduction that we 
meet with the most interesting phases of the life-history of the Vorticella. 
These are four in number, viz., fission, gemmation, encystation, and 
acinetation. The first of these, fission or self-division, is by far the most 
frequent, and I have witnessed it many times. When this is about to 
take place, an adult bell begins to alter its shape, becoming first globular, 
This will be illustrated in a subsequent number. 
