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Show 1888.] THE CARPUS AND TARSUS OF THE ANURA. 143 aid and advice always most cheerfully given ; while we have to tender thanks to Prof. W . K . Parker for useful specimens, to Prof. Wiedersheim of Freiburg for the limbs and a larva of Pipa, to Prof. W . N. Parker for some exquisitely preserved tadpoles of the C o m m o n Frog, and to Dr. G. Baur, of N e w Haven, Conn., for suggestions and advice. Some of our best results have been obtained from feet in which ossification was just commencing (ex. fig. 5). At this stage the outlines of the cartilages are more clearly defined than at the earlier ones (cf. fig. 9), while there is a total absence of any distortion or displacement consequent upon complete ossification (cf. figs. 5 & 6). Identification of this stage by external appearances is very difficult; absolute size, moreover, gives no clue to it, for while in a Xenophrys measuring 27 millim. from mouth to vent (fig. 14) all expectations were realized, in a Brachycephalus of 20 millim. ossification was found to be complete. d. Methods.-We early discarded the section-cutting method employed by Born (3, 6), chiefly because the results finally arrived at were less satisfactory than those obtainable from clarified preparations. Clarification in potash solution (kindly suggested to us by Prof. Wiedersheim) was tried, but relinquished, chiefly on account of the difficulties experienced in mounting the preparations. Better results were arrived at by clarifying in a mixture of glycerine and potash, and mounting permanently in glycerine jelly ; but our best results were all obtained by the use of clove oil, which offers additional advantages in allowing the preparations to be stained. Borax-carmine solution proved most serviceable as a dye; less successful preparations were, however, obtained with picro-carmine, hsematoxylin, and bismarck-brown. Our method of procedure was generally as follows : - T h e limb having been carefully skinned, the larger muscles were dissected off, in order to facilitate staining. The preparation was next immersed for about ten minutes in borax-carmine, and then transferred to acid alcohol (75 parts alcohol, 3 parts H N 0 3 , and 22 parts water), in order that superfluous stain might be removed; after dehydration in absolute alcohol, it was allowed to remain in oil of cloves. The final process consisted in carefully picking away the soft parts, little by little, with two pairs of small forceps under a simple microscope, while the preparation was still immersed in a glass trough of clove oil. The smaller preparations were ultimately mounted in Canada balsam. The above method admits of an examination of all parts in the undisturbed state, and consequently of an accurate determination of the relationships of apposed surfaces, such as is not possible with any other. Moreover, in that ossific centres, lines of fusion, furrows, or outstanding processes are rendered equally obvious, it is manifestly not open to objections which might conceivably arise out of exclusive reliance upon the section-cutter's art. 11* |
