Observations on British Zoophytes. 381 
chjma of the body supporting it are drawn out into a long 
thin process. When the animal issues from its tube, it pro- 
trudes its ciliary organ as a fleshy column, fringed on one 
side by a row of very long motionless cilia, but in an in- 
stant the column is twisted into a spiral, and the cilia are set 
in violent motion, urging currents of water towards the 
mouth. The marine species approaches in character, as to 
its rotatory organ, to C. MuUeri, while it inhabits a mucous 
tube like that of C. Mucicola. 
6. Oocytricha longicaudata. (PI. XIX. figs. 7, 8.) 
This remarkable animal, resembling very much Oxytricha 
retractilis, described by Claparede and Lachmann, was found 
in great numbers with Chcetospira maritima. The tail in this 
species is fully twice as long as that of Oxytricha retractilis, 
and is dragged after the swimming animal like a trailing 
rope, when suddenly the extremity of the tail is fixed by 
the long cilia at its extremity, and the Oxytricha, by violent 
contractions of its tail, jerks itself backwards and forwards 
in the most violent manner. The structure of tail, under 
an excellent power of eighty diameters, presents a peculiar 
striated and plaited appearance, like that of voluntary mus- 
cular fibre, but I could not make anything of it under higher 
powers. 
Description of Flute XVII. 
Figs. 7, 8. — Acharadria larynx. 
Description of Plate XVIII, 
Zooteirea religata, seen by black-ground illumination, and focussed for the 
centre of the " endosarc ;" a, with palpocils extended and curved by an 
upward current of water ; b, emerging from its cell ; c, retracted within its 
cell. 
Description of Plate XIX. 
Fig. \.—Zooieirea religata, with palpocils partially extended, and tubular con- 
tractile pedicle distended by water ; «, ectosarc ; b, endosarc ; c, tube ; 
d, muscular band ; e, areolar fibres ; /, gelatinous cell. 
Fig. 2. — Young Freya producta building its tube. 
Fig. 3. — Freya producta witli lengthened tube ; a, old mouth of tube ; b, thick- 
ened part of body from which the tube is secreted. 
Fig. 4 — Freya obstetrica ; a, nucleus. 
Figs. 5, 6. — Freya stylifer, extended, and in its cell. 
Fig. 7. — Oxytricha longicaudata, with tail extended. 
Fig. 8. — ,, with tail contracted. 
