X LIST OF ILLUSTRATIONS 



I-'IG. PACK 



22. Section of the Segmented Egg . 1 1 1 



22A-25A. Formation of the Mesenteron . . Bet-ween pages 112 and 113 



[Figures 23 to 37 refer to (he embryo at various stages."] 



23. Sagittal section (commencement of invagination) . . . .112 



24. Sagittal section {formation of 'mesenteron) 113 



25. Sagittal section (completion of mesenteron) . . . . . .114 



26. Transverse section (stage with open neural groove) . . . .118 



27. Sagittal section (blastopore open, neural groove closed) . . .119 



28. Sagittal section (stage of Fig. 20, 3 ) 120 



29. Sagittal section (stage of Fig. 20, e) . 121 



30. Transverse sections (development of eye) . . . . . .124 



3OA. Pharynx, ear and heart ...... To face page 129 



31. Diagram of 'branchial vessels and pronephros (stage 6.5 mm. long) . 131 



32. Diagram of heart and branchial vesse Is (stage 6. 5 mm. long) . . 132 



33. Dissection of a 12 mm. tadpole ........ 134 



34. Diagram of heart and branchial vessels (stage 12 mm. long) . . 135 

 34BIS. The tadpole's Skull ...... To face page 141 



34A. Skull of tailed frog ....... To face page 142 



35. Dissection of a 40 mm. tadpole . . 144 



36. Dissection of Urinogenital system (stage of Fig. 20, 9-10) . . . 146 



37. Transverse section at time of hatching (stage of Fig. 20, 2 ) . . 147 



38. Section of the cardiac end of the dog' s stomach 155 



39. Diagram of the phases of cell-division by mitosis (after Parker 1 } . 167 



40. Diagram slioivinrj the mode of reduction in the number of chromosomes 



(after Wilson) 171 



