Weber, in his classical memoir entitled “De aure et auditu Hominis et Animalium, Pars i., De aure Animalium aquatilium,” published in 1820, was the first to show that in certain families of Physostomous Teleostei, viz., the Siluridæ and Cyprinidæ, there exists a peculiar connection between the auditory organ and the air-bladder, by means of a chain of movably interconnected ossicles. To these two families, and to three others, viz., the Characinidæ, Gymnotidæ, and Gymnarchidæ, in which this singular mechanism was subsequently discovered, Sagemehl (33) applied the collective name of Ostariophyseæ (
oσταρiov
, ossicle;
ϕvσŋ
air-bladder), for the reason that the possession of this highly specialized mechanism implied community of descent. Since the publication of Weber’s memoir, various contributions to this subject have been made, but deal for the most part either with special features, or with individual species, or with a very limited number of species in particular families. In no single family of Ostariophyseæ has any attempt at present been made to institute a systematic and comparative examination of any considerable number of genera, and, at the same time, to deal with the various modifications which pertain to the air-bladder, auditory organ, and skeleton as correlated and mutually dependent factors. With regard to papers on such special points as the nature of the “complex” vertebra and the homologies of the Weberian ossicles, reference may be made to the contributions of Baudelot (1), Grassi (17), and Nusbaum (29), and to a recently published and valuable paper by Sörensen (37), which treats of certain skeletal modifications, not only in the Ostariophyseæ in general but in other Teleostei. Of papers dealing with other special points, the contributions of Hasse (19) and Nusbaum (
loc. cit.
) to the anatomy of the auditory organ must also be mentioned. Of individual families, the Siluridæ have received but little attention. Sagemehl’s paper deals mainly with the air-bladder of the Characinidæ. The papers of Grassi, Baudelot, and Nusbaum relate almost exclusively to the Cyprinidæ. The valuable observations of Sörensen, while more extensive as regards the families included within the range of his investigations, are nevertheless restricted to certain special features, and, apart from the development of ossifications in its walls, have but scanty reference to the air-bladder, or to the Weberian ossicles, or to the auditory organ in the relatively few Siluridæ described by him. Weber (
loc. cit.
) himself only described the air-bladder and the ossicles which bear his name in a single species (
Silurus glanis
). Johannes Müller, in his various contributions to the Berlin Academy during the years 1843-45, added somewhat to our knowledge of these structures, and notably by his discovery of the “elastic-spring” apparatus, but Müller’s attention was mainly directed to the grosser features in the anatomy of the air-bladder, to the entire exclusion of all but the slightest reference to the important skeletal modifications which are associated with the peculiar structure of that organ in the Siluridæ, or to the auditory ossicles. Reissner (32) has given a fairly complete account of the singular bone-encapsuled air-bladder of
Rhinelepis
, but among the most valuable of recent contributions to this branch of vertebrate morphology are the papers by Professor Ramsay Wright relating to the aberrant Siluroid
Hypophthalmus
(44), and to the more normal North American species
Amiurus catus
(42, 43), to which reference will subsequently be made. In this connexion reference may also be made to the numerous scattered references to the air-bladder of the Indian Siluridæ contained in the papers of the late Dr. Francis Day (9, 10), which, although often too brief, in several instances at any rate are valuable as throwing some light on the degenerate condition of that organ in certain rare abnormal forms. It is remarkable that this important family of Fishes has so little occupied the attention of morphologists, especially when we take into consideration the interesting modifications which its various members have undergone, and the fact that in this family the air-bladder and “auditory” ossicles are subject to greater variations, and are more highly specialized than in any other group of Ostariophyseæ. Probably the main reason why the Siluridæ have been so much neglected is due to the fact that they are principally tropical in habitat, or live in remote and inaccessible districts. Investigators at home are consequently dependent upon the exertions of collectors, who, as a rule, do not pay much attention to Fishes, and the relatively few species which do find their way to Europe are required for museum specimens. Fortunately for us we had the opportunity of purchasing the third series of the Siluroids collected by that eminent ichthyologist, the late Dr. Bleeker, who had amassed a magnificent collection of East Indian Fishes, amongst which the Siluridse were well represented. Subsequently we added to our collection what other specimens we were able to procure, especially African and South American species.
Extraordinary Sequence Diversity and Promiscuity of Centromeric Satellites in the Legume Tribe Fabeae