OUTLINES OF THE DEVELOPMENT OF THE TUATAEA. 83 



Fi{^. 23. — Through the anterior enclosed part of the alimentary canal, 



in front of the coelomic space, which will give rise to tlie pericardium. 



Fig. 24:. — Through the coelomic space {P.C.), which will give rise to the 



pericardium. 

 Fig. 25. — Just behind the opening into the anterior enclosed part of the 



alimentary canal. 

 Fig. 26. — Through the anterior end of the notochord. 

 Fig. 27. — Just behind the spot where the front end of the embryo, 

 enclosed in the pro-amuion, becomes free from the underlying blasto- 

 derm (compsre Fig, 35, Tr.L.). 

 Fig, 28, — Through the trunk region. 

 Fig, 29. — Through the trunk further back, showing the very small 



amniotic cavity overlying the medullary groove. 

 Fig. 30. — Through the posterior amniotic opening, showing the two up- 

 rising folds of the amnion not yet united. 

 Fig. 31. — Just in front of the primitive streak. 

 Fig. 32. — Through the ueurenteric canal {N. En.). 

 Fig. 33. — Embryo 64. Transverse section just in front of the posterior 

 amniotic opening. Zeiss C, ocular 1. 



Fig, 34. — Embryo 64. Transverse section through the posterior amniotic 

 opening and primitive streak, showing the primitive groove (P. G.). Zeiss C, 

 ocular 1, 



Figs. 35—46. Stage F, 



Fig. 35. — Embryo 61. Median longitudinal vertical section, slightly dia- 

 grammatic. 



Fig. 36. — Embryo 61. Similar section a little to one side of the middle 

 line. 



Fig. 37. — Embryo 72, seen from above, with portion of surrounding 

 blastoderm ; drawn from spirit specimen as an opaque object, the front part 

 of the embryo being seen through the overlying blastoderm of the area pel- 

 lucida. X 10. 



Fig. 38. — Embryo 72, seen from below after removal of the sub-embryonal 

 membrane and adherent yolk; drawn as before, x 10. 



Fig, 39. — Embryo 72, seen from above as a transparent object, after staining 

 with borax carmine and clearing in oil of cloves. The front part of the embryo 

 is seen through the overlying blastoderm. Zeiss A (with bottom lens re- 

 moved), ocular 1. 



Fig. 40. — Embryo 61, seen from above, with portion of the surrounding 

 blastoderm ; drawn from spirit specimen as an opaque object ; the front part 

 of the embryo seen through the overlying blastoderm of the area pellucida. 

 X 10. 



Fig. 41. — Embryo 61, seen from above as a transparent object, after staining 



