resemblance which is thus shown to a group of mammals, the Monotremata. This group includes only the Duck-billed Platypus of Australia and the spiny Anteater (Echidna) of the same continent and New Guinea. In both of these animals the heart valve in question is also largely muscular, and does not entirely encircle the opening from the auricle. These two mammals also, as everyone knows by this time, have the strange habit for a mammal of laying eggs, which is one among some other reasons which once led naturalists to place them in the neighbourhood of birds. The egg-laying, of course, is not distinctive, since reptiles have the same way of bringing forth their young; and as to the heart valve, it is rather to be explained by the fact that both types of animals are low in the scale of their respective groups, and therefore both approach a common ancestral form. Voice Organ. [Illustration: FIG. 15.--SYRINX OF RAVEN (POSTERIOR SURFACE). _g_, tympaniform membrane.] [Illustration: FIG. 16.--SYRINX OF RAVEN (LATERAL VIEW). _a_, _b_, _c_, _e_, _f_, intrinsic muscles; _d_, sterno-tracheal muscle.] [Illustration: FIG. 17.--SYRINX OF RAVEN CUT OPEN LONGITUDINALLY. _i_, pessulus; _h_, vibrating membrane; _g_, membrana tympaniformis.] By their voice, too, birds are distinguished from the rest of the animal creation. Though there may be legends of singing serpents and of talking monkeys, a harsh scream or a growl is the only manifestation of the emotions through the voice which exists until we arrive at man. Among birds, the possession of a melodious voice is limited to that group which we term the Passeres. Other birds can scream or utter a dull note, while many are mute. So flexible is the voice organ of these creatures that they are the only animals that can imitate human speech. Here, however, it is not only the Passeres which can imitate the essential attribute of man. The Parrots, of course, are always supposed to be _the_ birds which can talk, but this is far from being the truth. The hoarse utterances of most Parrots are left far behind in clearness of sound and correctness of imitation by the little Indian Mynah, which may be usually seen at the Zoological Gardens, and heard to speak. But the Parrot cannot sing. These are the only two groups of birds which have so elaborate and flexible an organ of voice. From this it might be inferred that some peculiarities of mechanism would distinguish the organ in question of these birds, and that is what we actually find to be the case. But, oddly enough, it is not only those birds which have a beautiful voice whose voice organs are so elaborate in structure. The harsh croak of the Raven issues from a syrinx which is as delicately fashioned as that which allows of the exquisitely varied tones of the Nightingale. The word ‘syrinx’ has been mentioned; that is the technical term for the voice organ of the bird, which is