1, Rhyncheta cyclopum, Zenker; only a single tentacle and that suctorial; epizoic on Cyclops.

2, Sphaerophrya urostylae, Maupas; normal adult; parasitic in Ciliate Urostyla.

3, The same dividing by transverse fission, the anterior moiety with temporarily developed cilia.

4, 5, 6, Sphaerophrya stentorea, Maupas. Parasitic in Stentor, and at one time mistaken for its young.

7, Trichophrya epistylidis, Cl. and L.

8, Hemiophrya gemmipara, Hertwig. Example with six buds, into each of which a branch of the meganucleus a is extended.

9, The same species, showing the two kinds of tentacles (the suctorial and the pointed), and two contractile vacuoles b.

10, Ciliated embryo of Podophrya steinii, Cl. and L.

11, Acineta grandis, Saville Kent; showing pedunculated cup, and animal with two bunches of entirely suctorial tentacles.

12, Sphaerophrya magna, Maupas. It has seized with its tentacles, and is in the act of sucking out the juices of six examples of the Ciliate Colpoda parvifrons.

13, Podophrya elongata, Cl. and L.

14, Hemiophrya benedenii, Fraip.; the suctorial tentacles retracted.

15, Dendrocometes paradoxus, Stein. Parasitic on Gammarus pulex; captured prey.

16, A single tentacle of Podophrya. R. Hertwig.

17-20, Dendrosoma radians, Ehr.:—17, free-swimming ciliated embryo. 18, Earliest fixed condition of the embryo. 19, Later stage, a single tentaculiferous process now developed. 20, Adult colony; c, enclosed ciliated embryos; d, branching stolon; e, more minute reproductive (?) bodies.