PH YSOPHORID^. I 5 3 



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. Yelella 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 reahsed 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 tl^e 

 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 

 tlirowing 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 ext8nd it itself and withdraw at 

 pleasure. A tentacle of Velella sufficiently compressed presents a 

 surface brisding 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 Velellae have their javelins, as the Greek 

 and Roman warriors had, and a lasso, as the cavaliers of Mexico and 

 Texas have. 



'J'he reproductive individuals form the great mass of the appen- 



