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Show 496 PROF. HOWES AND MR. A. M. DAV1ES ON THE [Dec. 4, observation of Peters's (16), as to the existence of " a small additional phalanx between the ultimate and what is normally the penultimate " one in his Polypedatince. Peters's description was very meagre, and it is to Boulenger that credit is due for having placed the matter on a sound footing. The conclusions arrived at by the two authors differ in important respects, and these we shall duly consider. Both deal exclusively with the Ranidce. The presence of a structure in the Hylidce which at once suggests that in question had heen previously noted by one of us, while engaged upon an allied investigation (7), and as we had, in pursuit of the same, accumulated material sufficient for a fuller elucidation of the problem, we decided to work it out. W e give in Section IV. a complete list of the animals examined. Our sincere thanks are due to Dr. Gunther, F.R.S., for certain of these, and to Mr. Boulenger for others and for ever generous assistance and advice. Method.-The digits were, if necessary, first decalcified in \ p.c. chromic-acid solution, with a few drops of nitric acid. When soft they were transferred to an aqueous solution of N a H C 0 3 until the acid was for the most part removed. They were then dehydrated with alcoholic solutions of increasing strengths and stained inborax-carmine, the excess of stain being subsequently removed by 75 p. c. alcohol, to which a few drops of H N 0 3 were added. They were then finally dehydrated in absolute alcohol and transferred, via turpentine, to paraffin, and cut with the Rocking Microtome. Staining was, in many instances, resorted to without dehydration. W e found that a couple of hours sufficed in most cases for decalcification in chromic and nitric acids. The preparations were removed from this as soon as possible, for it was found that if allowed a prolonged immersion therein the chances of successful staining became reduced. In deciding upon the above method we found Whitman's * Methods of Research' of great service, and we gladly acknowledge the help afforded us by that work. II. GENERAL AND ANATOMICAL. The supernumerary phalanx was, as seen by both Peters and Boulenger, ossified, and in such a condition that, had it been found fossil, would have left no doubt of its value as such, except perhaps for its small size. It will be shown later on that the structure is subject to a wide range of modification anatomically and histologically ; and its fundamental relationships may best be studied in detail in such a form as the tree-frog (Hyla arborea, Plate XXIV. fig. 1). Neither Peters nor Boulenger were aware of its existence in this family ; and we find that our own discovery of the same was anticipated by Leydig; in 1876. He writes (14. p. 166), "von Andern und mir wurde bei Hyla arborea ein sich zwischen die letzte und vorletzte Phalanx einschiebender Knorpel erwahnt." This author, then, has a long priority of claim to the first discovery. The supernumerary phalanx is, in the adults of most forms in which |