THE FROG. 27 



PLATE VII. 



THE FKOG. EMBRYOLOGY AND LARVAL METAMORPHOSES. 



FIG. I. The segmenting ovum, on the appearance of the first cleavage farrow. 

 FIG. I 11 .* Section of the same, at right angles to the furrow. 



FIG. II. The same, on the appearance of the second furrow, viewed slightly from 

 above. 



FIG. II a . The above, seen from beneath. 



FIG. III. The same, on the appearance of the third first horizontal furrow. 



FIG. III" 1 . The same, seen from above. 



FIG. IIP*. Longitudinal section of the same. 



FIGS. IV". and IV'. Two phases in the segmentation of the ovum, on the appearance 

 of the fourth and fifth furrows. 



FIG. V,* Longitudinal vertical section, at a slightly later stage than the above. 



FIG. VI.- A later stage. The upper pigmented pole is seen to be dividing more 

 rapidly than the lower. 



FIG. VII. A still later phase in the same. 



FIG. VII ft . Longitudinal vertical section of Fig. VI F. 



FIG. VIII. The segmenting ovum, at the blastopore stnge. 



FIG. VIII a . Longitudinal vertical section of the same. 



(Figs. VII". and VHP. x 10. All the others x 5.) 



Eauber (20) has recently made an elaborate study of the details of the early segmenta- 

 tion of the Frog's ovum. 



FIG. IX. Surface view at a stage somewhat later than Fig. VIII. 

 The medullary folds are seen to be approximating at one point ; they finally meet 

 there and continue to close in opposite directions, as indicated by the arrows, x 10. 



FIG. X. The young tadpole, at the first appearance of visceral arches. Dorsal view. 



' The nuclei of these figures are diagrammatic ; they are only occasionally visible in cells so large. 



