498 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



Fig. 22. View from below of a high-arched 16-celled stage, showing 9 cells in the 

 first tier, 6 in the second, and 1 keystone, together with the large seg- 

 mentation cavity. 



23. Nearly normal 82-celled blastoderm. 



24. Irregular 27-celled blastoderm. Cells in three tiers, blastoderm thickest at 



lower edge. 



25. Irregular 28-celled stage. Cells in three tiers, blastoderm highest in center. 



26. Divided 32-celled blastoderm, 14 cells in smaller, 18 in larger division, both 



resting on a common protoplasmic basis. 



27. Later stage, with 38 cells, showing the growing irregularity of the segmenta- 



tion. 



Plate VII. 



28. Section through germ disc, 5 hours in water. Below the dotted line yolk 



and protoplasm are mixed. 



29. Section through germ disc, 11 hours and 20 minutes in water, showing 



formation of buds. 



30. Section through germ disc 262 hours in water. 



31. Section through germ disc 36-48 hours in pouch. 



32. Section through center of 1-celled stage like fig. 1, Plate V. 



33. Section through 2-celled stage. Protoplasmic fibrils at right angles to the 



plane of the furrow. 



34. Stage of 2 cells, section through a-h of fig. 2. 



35. Irregular 2-celled stage, section through a-h of fig. 3, showing vesicle at 



base of furrow. 



36. Two-celled stage, furrow taking form of narrow cleft. 



37. Furrow of 2-celled stage formed by breaking down of walls of vesicles 



lying in a vertical series. 



38. Horizontal section through 4-blastomere stage of fig. 4. 



39. Stage of 8 cells, section through plane a-h of fig. 7. 



40. Stage of 8 into 16 cells, section through c-d of fig. 7. 



41. Eight-celled stage, section at right angles to long axis of such stages as figs. 



7 and 8, showing protoplasmic bridge. 



42. Stage of 8 cells, section in plane a-h of fig. 10. 



Platk VIII. 



43. Eight-celled stage, section through a-h of fig. 12 showing a protoplasmic 



bridge. 



44. Sixteen-celled stage, section in plane a-h of fig. 17. 



45. Stage of 16 cells, section through plane a-h of fig. 16. 



46. Stage of 16 cells, section in plane a-h of fig. 18. 



47. Sixteen-celled stage, section through blastoderm like fig. 19. 



48. High-arched 16-celled stage, section through l)lastoderm like fig. 22, with 



large segmentation cavity. 



49. Stage of 32 cells, section through a blastoderm like fig. 23. 



50. vStage of 32 cells, high-arched tyi)e, section is through a-h of fig. 24. 



51. Stage of 32 cells, thick-ended type with lai'ge segmentation cavity and thin 



central periblast. 



52. Stage of 32 cells, section through a high-arched blastoderm similar to fig. 25. 



53. Thirty-two-celled stage. No penblast; two tiers of cells cut out of a solid 



mass of protoplasm. 



54. Divided 32- to 64-celled stage. No periblast; basal protoplasm thick, with 



many vacuoles, and having cell walls cutting down into it. 



