ON THE PROGRESS AND PRESENT STATE OP ORNITHOLOGY. 207 



the air -cavities of the bones are highly developed, in order to compensate for 

 the shortness of the wings. He adds the important remarlt, that " when once 

 the object of aerial flight is abandoned, the wings are reduced to exactly that 

 size which is most efficient of all for subaquatic progression ; species of an 

 intermediate character of course never occurring." This principle of the ne- 

 cessity of hiatuses in the natural system (of which numerous other examples 

 might be adduced), is one which I have long regarded as conclusive against 

 that continuity of affinities and symmetry of arrangement Avhich some writers 

 have endeavoured to demonstrate. 



Mr. T. AUis of York (whose beautifully prepared ornithic skeletons now 

 in the York Museum are so highly creditable to his skill as an anatomist) has 

 made some observations on the connexion between the furculum and sternum, 

 showing that in certain birds possessing powers of long-continued flight these 

 bones are connected by an intimate symphysis, which in Pelecanus and Grrus 

 amounts to an actual anchylosis. (Zool. Proc, 1835). 



The anatomies of Pelecanus, Dicholophus and Corythaix, are described in 

 detail by Mr. W. Martin in the work last quoted. 



A paper on the anatomy of Corvus corone by M. Jacquemin, will be found 

 in the ' Isis,' 1837, and the osteology of the Trochilidm is described by M. J. 

 Geoffroy St. Hilaire in 'Comptes Rendus,' 1838*. 



Several points of ornithic anatomy are treated of by Prof. Wagner in the 

 'Abhandl. der Baierischen Akad.,' 1837, and the osteology of the genera 

 Crypturus, Dicholophus, Psophia and Mycteria, is fully described. The struc- 

 ture of the Struthionida is beautifully portrayed by D'Alton in his ' Skelete 

 der Straussartigen Vogel,' 1827. 



There is a paper by M. Schlegel on the supposed absence of nostrils in the 

 genus Sula, in the ' Tijdschrift voor natuurlijke Geschiedenis,' 1839, of which, 

 from being unacquainted with the Dutch language, I regret my inability to 

 give a summary. 



The osteology of several groups of Natatores is treated of by M. Brandt in 

 an elaborate and highly important paper in the ' Memoires de I'Acad. Imp. de 

 St. Petersbourg,' 1839. The researches of this author throw great light upon 

 the classification of many obscure groups, and nothing can be more exact than 

 his figures and descriptions of ornithic osteology. 



Mr. Yarrell has paid considerable attention to the subject of hyhridity 

 (Zool. Proc, 1832, 1836, &c.). The result of his observation seems to be 

 that hybrid birds will occasionally propagate with the pure race on either 

 side, but rarely, if ever, with each other, thus indicating a special provision of 

 nature to preserve the distinctness and permanency of species. Mr. Eyton 

 and Mr. Fuller have also made notes on the same subject (Zool. Proc, 1S35). 

 See also a paper by Mr. W. Thompson in the 'Mag. of Zool. and Bot.,' vol. i. 



Mr. G. Gulliver, who has made a series of microscopic researches into 

 the blood-corpuscles of the Vertebrata, taking exact measurements of these 

 minute bodies in different genera and species, has in the course of this in- 

 quiry given a fair share of attention to the corpuscles of birds, and his la- 

 bours are recorded in the ' Proceedings of the Zool. Soc.,' 1842, &c. 



The difficult question of the influence of climate in producing permanent 

 varieties of species is discussed by Dr. C. L. Gloger in a treatise published at 

 Breslau,1833, and which deserves translation for the use of British naturalists, 

 although the author carries his theory to too great an extent. 



The arrangement of the feathers on birds, to which attention was first 



* The ' Disquisitiones Anatomicae Psittacorum,' by M. Thuet, Turin, 1838, and Kuhlraan's 

 dissertation, ' De Absentia Furculse in Psittaco PuUario,' KieJ, 1842, ai'e works which I have 

 not seen. 



