26 ZOOLOGY 
of a spherical form, and grooved on one side like a peach. From 
the bottom of this groove a very large transversely-striated 
flagellum takes its origin. Near the base of the flagellum is 
the mouth, opening into a sort of pharynx; a second smaller 
flagellum has its origin in the latter. The protoplasm of the 
globular body is very reticulate. No contractile vacuole has 
been observed. At times octiluca withdraws its flagella 
and passes into a resting condition, but it does not form a cyst. 
This animal is interesting, as it is phosphorescent, and gives rise 
to a large part of the phosphorescence of temperate seas. The 
seat of the lght is said to be the superficial protoplasm. 
teproduction is by fission, but motile swarm-spores are also 
formed in large numbers. Conjugation has been observed. 
Cuiass III. Giliata. 
This class is characterised by the possession of cilia as 
locomotor organs, arranged either in a perioral ring, or forming 
a more or less complete covermg. A nucleus is always present ; 
this may be single, and is then accompanied by a paranucleus, 
or it may be distributed in small fragments throughout the 
body. One or more contractile vacuoles are present. The 
shape of the body is very various. Some Ciliata are united 
into colonies, and some form gelatinous tubes in which they 
live; the majority, however, are free-swimming. Conjugation is 
common, but usually does not end in permanent fusion. Fission, 
usually simple, but sometimes multiple, is the usual method of 
reproduction. 
This class has been divided into four Orders, characterised 
by the arrangement and nature of the cilia. 
Order I. Peritricha.—Cilia arranged in an anterior ring 
or spiral, to which a posterior ring may be added. The rest of the 
body wnerliated. 
Torquatella has its cilia fused to one another, and so a 
vibratile membrane is formed which surrounds the anterior end. 
Trichodina is very common, crawling on the tentacles and body- 
wall of Hydra; it is pyramidal in shape, and has two circlets 
of cilia. On its sucker-like base a curious horny toothed ring 
is situated. 
