DR. A. FARRE ON THE STRUCTURE OF THE CILIOBRACHIATE POLYPI. 401 
They do not appear to answer any purpose in the economy of the animal ; and from 
their persistence after its death, they would seem to have the power of resisting 1 those 
forces which cause the decomposition of the other parts. It is most probable that 
they are connected with the process of reproduction, but whether they may be viewed 
as ovaries or as immature ova, and what relation the white and brown bodies have 
to each other, are considerations that might be reserved for further opportunities of 
elucidation. I have never detected any motion in the granules of which they are 
composed. 
PLATE XXII. 
Vesicularia spinosa, Thompson, Zool. Research. Mem. V. pi. iii. 
Syn. Corallina confervoides, Ellis, Cor. pi. xi. N. 17 . b. B.C.D. 
Sertularia sericea, Pall., El. Zooph. p. 114. No. 65. 
Sertularia spinosa , Linn., Gmel. p. 3855. No. 23. 
Valkeria spinosa , Flem. Brit. Anim. p. 551. Gen. lxx. 198. 
This species forms part of the subject of Mr. Thompson’s memoir, whose name for 
it I have adopted. In this memoir, which contains but a very rough sketch of the 
animal, he calls the part that I have described as a gizzard the stomach, which 
latter organ he mistook for an ovarium. 
It might be difficult to select two species differing more in external characters than 
do this and the previous one, yet in the structure of the animal hardly any essential 
points of distinction can be observed : it is one of the smallest and most delicate 
species on our coast. The main stem, which is zig-zag, (fig. 1.) sends from each 
angle two branches that divide dichotomously to their extremities, which in growing 
branches are rounded, but in others sharp and spiny ; a circumstance that did not 
escape the notice of Ellis. The vesicles are so minute that they can with difficulty 
be detected by the naked eye. The animal has but eight arms, (fig. 3.) which are 
short and stiff, and during expansion remain nearly motionless in the usual funnel- 
like form, but may be occasionally seen separated so far from each other as to stand 
out at nearly right angles from the body: they are ciliated, but not armed with 
spines. The alimentary canal presents the same character as that already described 
in Bowerbankia ; but allowing for the much smaller size of the animal, is proportion- 
ately shorter and stouter. 
The muscular apparatus consists of the gastric and tentacular retractors, the former 
(fig. 8. a.) arising from the bottom, the latter, (8. b.) a little above from the side of 
the cell; two rows of parietal muscles (fig. 8. c.), and two sets of operculum retractors 
(fig. 8. d.), in which respect it differs from the former species, where there are three 
double sets ; and the triangular indentation at the upper part of the closed cell is 
consequently wanting. The cell is also much broader in proportion to its length, 
having a more oval form. The operculum is finished by a row of setae. The connect- 
