"On a cursory view," says Dr. Johnston, "the polypodium of the three families embraced appear very dissimilar, and accordingly, by many recent authors, they have been scattered over the class, and placed widely asunder. The affinity between them, however, is generally acknowledged, and had been distinctly perceived by some of the earliest zoophytologists. Thus Bohadsch found so much in common in the typical pennatulæ and a species of _Alcyonium_, that he has not hesitated to describe them as members of the same genus; and, although the more systematic character of Pallas prevented him from falling into this error, if error it can be called, he did not the less recognize the relationship between the genera or families. Pallas also tells us that his _Pennatula cynomorium_ differs from the _Alcyonium_ only in this, that the former is a movable and the latter a fixed polypidom; and he saw with equal clearness the connection which exists between these genera and the shrub-like _Gorgonia_. Of the _Pennatula mirabilis_ he had doubts whether it was not rather a species of _Gorgonia_, until he perceived that the stem was attenuated at each end, and free; and of the Sea-pens generally, Ellis remarks that they are 'a genus of zoophytes not far removed from the _Gorgonias_, on account of their polyp mouths, as well as having a bone in the inside and flesh without.' 'On the other hand, the _Gorgoniæ_ seem,' says Pallas, 'with the exception of their horny skeleton, to be nearly similar in structure to the _Alcyonia_; but as there are species of _Gorgonia_ which are suberose internally, and almost of a uniform medullary consistence, even this mark of distinction fails to separate the tribes, and we have little left to guide us in arranging these esculent species excepting their external habits.'" "With most corallines," says Frédol, "the elementary individual, in spite of the adhesion established among them, possesses a vital energy all its own; it is in some respects quite independent. They have each its own particular will, which it is difficult to mistake for a common will; but it is not thus with the _Pennatula_. Their association consists of a non-adherent polyp, which moves--obscurely, it is true--but still it moves. To what does this lead? To this: that the parts which they possess in common, in place of being horny or calcareous--that is, completely inert--are fleshy, with contractile powers; that is to say, animated. Consequently, the polyp of the _Pennatula_ are less independent of each other than the coral polyp, which have a central, perhaps a sensible organ, common to all, which binds them to each other, giving a certain unity to their acts. The Coralline polyps have no will; the _Pennatula_ have." CHAPTER VII. ZOANTHARIA, OR ANIMAL FLOWERS.