ACALEPH^E. 231 



It is a general characteristic of all colonies of polypi that the 

 digestive cavities of the individuals composing them meet and inos- 

 culate in a common vascular system. The Yilellse present the same 

 conformation. Only in their 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 realized by Nature. 



The central polyp is alone destined to absorb the food. M. Yogt 

 has always found in its interior 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 ex- 

 tremity. These are strong muscular tubes of considerable thickness, 

 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 a sac with com- 

 paratively thick walls. If this sac is compressed under the microscope 

 it explodes, opening at a determinate part, and throwing out an 

 apparatus forming a long stiff filament, which is implanted on a conical 

 channel and surrounded with points. " I know not," says M. Yogt, 

 " if all this machinery can re-enter the capsule after it has exploded ; 

 but I presume that the animal can extend itself and withdraw at 

 pleasure. A tentacle of Yilella sufficiently compressed presents a 

 surface bristling with these 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 

 crustaceans 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 Yilellse have their javelins, as the Greek and 

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

 Texas have. 



The reproducing individuals form the great mass of the appendages 

 attached to the under surface of the Yilella. The form of the 

 individuals is much more varied, inasmuch as they are extremely 



