second bronchial rings (or in this part often semi-rings) being closely attached to the trachea, and the spaces between the second and third and the third and fourth being generally closed by an outer tympaniform (drum-like) membrane, while the rest of the semi-rings of the bronchi are closed by the inner tympaniform membrane. It should be clearly understood that all the notes emitted by Birds are produced by the above structures only, and that the tongue has nothing to do with their utterance, except, possibly, in the case of the sounds that Parrots (but not other birds) are taught to produce. CLASSIFICATION.–The Classification of Birds is still in a condition of uncertainty, notwithstanding the many schemes successively propounded during more than two centuries. To dwell upon them here would be impossible, and it is only practicable {14}to trace in the briefest way the line which has led to the most recent attempts, and to name those whose researches have produced the results which may be fairly regarded as attained. First among them is Nitzsch (1806-1840), to whom followed Merrem (1812-1817), and after a few years L'Herminier (1827). These three worked quite independently, and in their lifetime little notice was taken of their labours; for, though there were good ornithologists among their contemporaries, little value was then set upon internal characters in this connexion. An improvement took place when the great Johannes Müller (1846, 1847) published his scheme for grouping the _Passeres_, which, though based on purely anatomical facts, was almost immediately accepted, chiefly through the simultaneous exertions of Dr. Cabanis, by systematists of the Old School. For twenty years no advance was made, for the morphological researches of Parker were not directly taxonomical; but Huxley (1867, 1868) started what was practically a new line of investigation, though it subsequently appeared that up to a certain point it had been already suggested by Dr. Cornay (1842-1847). The impetus thus given was fortunately sustained, Huxley's example being followed by Dr. Murie, and by two promising men, A. Garrod and W. A. Forbes, both of whom died at an early age, leaving their mark in work which, though much of it was crude, was that of true genius. Mr. Sclater (1880) has tried to bring the results of the whole four into harmony with pre-existing views, and a similar attempt was that of Dr. Stejneger (1885); but all were overshadowed by the monumental performance of Prof. Fürbringer, whose _Untersuchungen zur Morphologie und Systematik der Vögel_, completed in 1888, must ever remain a record of unexampled labour, while his considerations on the derivation of Birds from Reptiles, and of the later groups of Birds from the earlier, whether his results be right or wrong, are of the utmost importance to the ornithologist. During the progress of this work the author was in frequent communication with Dr. Gadow, himself engaged on the ornithological portion