Illustrations xiii 



FIGURE PAGE 



21. Transverse Section through the Region of the 



Hind-Brain of a Young Tadpole . . 57 



22. Horizontal Section of a Tadpole at the Time 



of Hatching. (After Marshall) . . -59 



23. Diagrammatic Figures of a y-mm. Tadpole, 



Shortly after Hatching, Showing the Ar- 

 rangement of the Blood Vessels: A from 

 Below; B from the Side. (After Marshall) 63 



24. A i2-mm. Tadpole, Dissected from the Ventral 



Side. (After Marshall) .... 65 



25. Diagrams to Illustrate the Mode of Develop- 



ment of the Heart . . . 68 



26. A Diagrammatic Figure of the Head and Neck 



of a i2-mm. Tadpole, from the Right Side, 

 to Show the Heart and Branchial Vessels. 

 Gills and Gill Capillaries not Represented. 

 (After Marshall) 71 



27. Diagrammatic Figure of the Arterial System 



of the Male Frog, from Right Side. (After 

 Marshall) ....... 73 



28. A 4o-mm. Tadpole Dissected from the Ventral 



Surface. (After Marshall). ... 76 



29. A Tailed Frog, near the Close of Metamor- 



phosis, Dissected from the Ventral Surface. 

 (After Marshall) 80 



30. Diagrams to Illustrate the Development of the 



Head-Kidney. (Somewhat altered from 

 Morgan) ....... 82 



