232 
THE OCEAN WORLD. 
which has been very minutely examined by M. Charles Vogt, ol 
Geneva, from whose work on the “ Inferior Animals of the Medi- 
terranean ” our details are borrowed. V. spirane, sometimes called 
V. limbosa, was discovered in the Mediterranean, between Monaco 
and Mentone, by Forskahl, who most erroneously took it for a holo- 
tharia. On the upper surface of the animal is a hydrostatic apparatus, 
the object of which is to maintain its equilibrium in the ambient 
element. This apparatus consists of a shield and a crest, organs ol 
which M. Yogt gives a very detailed description; but it is on the 
under surface that the principal organs of the Vilella are exhibited. 
These are not seen when the animal swims, because under such 
circumstances the vertical, oblique crest only is visible. The lower 
surface is concave, with a sort of mesial nucleus, presenting at the ex- 
tremity of a trumpet-like prolongation, whitish and contractile, a sort 
of central mouth, surrounded by tentacular cirri, the external row 
being much loDger than the internal ones. This was formerly thought 
to be the stomach of the Vilella, In the present day, this appendage 
is known to be the central polype around which are grouped other 
■whitish and much smaller appendages, the base being surrounded by 
little yellow bunches. These are supposed to be the reproductive 
organs. Between the crest and the shield numerous free tentacles 
present themselves, vermiform in appearance, cylindrical, and of a sky- 
blue colour, which are kept in continual motion. 
The Vilella is therefore not an isolated individual, but a group or 
colony, in which the individuals intended to be reproductive are the 
most numerous, and occupy tho inferior parts. 
Tim central polype, by its size and structure, is distinguishable at 
the first glance from all the other appendages of the lower surface ol 
the body. It is a cylindrical tube, very contractile and pear-shaped, 
swollen into a round ball, or considerably elongated. Its mouth i 9 
round arid much dilated ; it opens in the cylindrical or trumpet part, 
which is contained in a sac in the form of elongated fusci, clothed 
in the whitish integuments which formed the body of the polype when 
perfect. At the bottom of tlie sac two rows of openings are observed, 
which lead to a vascular network extending over the whole body ; the 
membranous parts, while affecting various conditions in their arrange' 
ment, are nevertheless in direct communication with all the reproductive 
individuals. 
