THE FROG. 27 



PLATE VII. 



THE FROG. EMBRYOLOGY AND LARVAL METAMORPHOSES. 



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

 FIG. I*.* 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 ahove, seen from beneath. 



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



FIG. III*. The same, seen from above. 



FIG. IIP*. Longitudinal section of the same. 



FIGS. IV B . 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. VIP. Longitudinal vertical section of Fig. Vlf. 



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



FIG. VHP. Longitudinal vertical section of the same. 



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



Rauber (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 Pig. VIII. 

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

 there and contimie 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 nnelei of those figures are diagrammatic ; they are only occasionally visible in cells BO large. 



