AMPHIBIANS. 81 



Stage 3, Rana C. In a few days the young Frog's tail becomes reduced to a stump two lines 

 in length, whilst the waist has become slender, the fore legs longer and free, and the hind legs, 

 which were the shortest, are now considerably longer than the others. In company with myriads 

 of equally or still more ripe Fish-quadrupeds, it now seeks the dry land. At this time the 

 Sternum (which lies imbedded in connective tissue so crowded with black pigment-cells as to make 

 this particular demonstration the hardest in morphology) has grown into two notable lobes, 

 pointed at the fore end, rounded outside and behind, and straight at the mid-line (Plate V, 

 fig. 4, st., magnified seventy-five diameters). They nearly fill the angle between the epicoracoids, 

 and have grown very rapidly since the last stage, but the moieties are perfectly distinct. 

 In Plate V, fig. 5, the angle of the prae-coracoid (p. cr.) is shown, magnified seventy-five 

 diameters, and in front of the bony bar a small hillock of soft new cartilage is seen (o. st.) ; the 

 position of the same part on the opposite side is shown in outline ; it is continuous with the 

 cartilage inside the lower end of the prae-coracoidal bony bar ; this is the first rudiment of the 

 " omosternum," and answers morphologically to the persistent condition of Pipa and Pseudis 

 (Plate VI, figs. 1 and 7, o. st.). 



Stage 4, Rana D. In Plate V, fig. 6, the next condition of the Frog is shown (magnified 

 fifteen diameters) ; the figure represents the Shoulder-plates spread out, and seen from below. 

 The supra-scapula (s. sc.) is considerably broader above than in Rana A ; but the anterior bony 

 plate has not spread much. The scapula (sc.) has become twice as long, relatively, having crept 

 upwards towards the supra-scapular bony plate and downwards to the glenoid cavity (gl.). The 

 pra3-coracoid sheath (p. cr.) is only a quarter the distance from the scapula, and has covered more 

 of the cartilage, whilst the coracoid (cr.), which in figure 1 had its upper end the largest, is now 

 almost equally enlarged at both ends ; hereafter the lower end will be twice the size of the upper 

 (see fig. 11, cr.). The epicoracoid flap (e. cr.) is much broader, and overlaps near the Sternum ; 

 its posterior angle is well developed ; and the sharp upper end of the fenestra (cr. f.) has become 

 rounded, as arrested clefts are wont to do. The glenoid cavity (gl.) is relatively less, and its notch 

 has changed position in relation to the scapula, which now touches it. The soft projecting angles 

 of the prse-coracoid have not only become segmented from their root, but these freed moieties 

 have coalesced ; thus the " omosternum " (o. st.) is formed (a more enlarged drawing of which is 

 seen in fig. 7, magnified seventy-five diameters). This unossified simple keystone piece answers 

 to the persistent condition of MegalopJirys (see Plate VII, fig. 8, o. st.). 



The keystone of the hyoid arch is formed in exactly the same manner at a much earlier period 

 of the Frog's life. The Sternum itself (fig. 6, st., and fig. 8, st., the latter magnified seventy-five 

 diameters) has also become one by the complete coalescence of its symmetrical halves ; only a small 

 shallow notch on its xiphoid margin remains of the primordial boundary-line. But for this notch, 

 which is persistent, this low-conditioned Sternum would answer exactly to that of Dadylethra 

 (Plate VI, fig. 11, st.) : it also comes very close to that of Pipa (Plate VI, fig. 1, st.) ; but the 

 Sternum in that type suffers " endostosis." 



Stage 5, Rana E. As life is a " ceaseless motion," our perfected Batrachian is constantly 

 undergoing mass-changes and molecular changes ; and if examined a few weeks after its trans- 

 formation, its skeletal structure will be found to have acquired several new characters. 



Plate V, fig. 9, shows a first summer Frog's Shoulder-plate, as seen from above, and mag- 

 11 



