PHYVSOPHORID AE, 153 
which formed the body of the polyp when perfect. At the bottom 
of the 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 arrangement, are 
nevertheless in direct communication with all the reproductive 
individuals. 
It is a general characteristic of all colonies of polyps that the 
digestive cavities of the individuals composing them meet and in- 
.osculate in a common vascular system. Velella presents the same 
conformation. Only in this case the vascular system is extended 
horizontally, this being the essential character of the union of all the 
individuals constituting the colony, with the canals common to all, 
in which the nourishing fluids circulate, elaborated for all and by all. 
It is a true picture of social communism realised by Nature. 
The central polyp is alone destined to absorb the food. M. Vogt 
has always found in its internal cavity fragments of the shells of 
crustaceans, the remains of small fishes ; and he has often seen the 
hard parts which resist digestion discharged through the trumpet-like 
opening. ‘This central polyp nourishes itself and also all the others, 
but is itself sterile. 
The tentacles are hollow cylinders, completely closed at the 
extremity. They are strong muscular tubes of considerable thick- 
ness, the interior of which is filled with a transparent liquid. They 
are enveloped in a strong membrane of a deep-blue colour. The 
epidermis is furnished with small stinging capsules, formed of sacs 
with comparatively thick walls. If one of these sacs is compressed 
under the microscope it explodes, opening at a determinate part, and 
throwing out an apparatus in the form of a long stiff filament, which 
is slightly enlarged at its free end. “I know not,” says M. Vogt, 
“if all this machinery can re-enter the capsule after it has exploded ; 
but I presume that the animal can extend it itself and withdraw at 
pleasure. A tentacle of Velella sufficiently compressed presents a 
surface bristling with cirri, so as to resemble a brush. ‘The tentacles 
themselves are in continual motion, and I have no reason to doubt 
that the observation of Lesson, who saw them cover small crusta- 
ceans and fishes, may be perfectly true. These stinging organs 
doubtless serve the same purpose as with other animals of the same 
class; namely, to kill the prey which the tentacles have enabled 
them to secure.” Thus the Velellz have their javelins, as the Greek 
and Roman warriors had, and a lasso, as the cavaliers of Mexico and 
Texas have. 
The reproductive individuals form the great mass of the appen- 
