OUTLINES OF THE DEVELOPMENT OY THE TUATAUA. 85 



incompletely formed dorsally, leaving a slit-like opening {dni.S.) into the 

 amniotic cavity.) 



Fig. 55. — Embryo 46. Transverse section through the dorsal amniotic 

 opening, a little in front of the neurenteric canal. Zeiss A, ocular 1. 



Fig. 56. — Embryo 44, seen from above as an opaque object in spirit, with 

 portion of surrounding blastoderm. The embryo itself is seen dimly through 

 the foetal membranes. X 10. 



Fig. 57. — Embryo 44, drawn from below, as before, x 10. 

 Fig. 58. — Embryo 44, seen from above through the foetal membranes as a 

 transparent object, after staining with borax carmine and clearing in oil of 

 cloves. Zeiss A (with bottom lens removed), ocular 1. 



Fig. 59. — Embryo 44, anterior half, drawn from below as before. Zeiss A, 

 ocular 1. 



Figs. 60 — 72. — Transverse sections of embryo 44, arranged in order; drawn 

 under Zeiss A, ocular 1. 



Fig. 60. — Through the fore-brain, where the left half of its roof overlaps 



the right. 

 Fig. 61. — Through the optic vesicles of the paired eyes. 

 Fig. 62. — Through the anterior enclosed part of the alimentary canal in 



front of the stomodseum. 

 Fig. 63. — Through the stomodseum and hind brain. 

 Fig. 64. — Through the hind brain and auditory pits. 

 Fig. 65. — Through the first pair of mesoblastic somites, heart and peri- 



cardium. 

 Fig. 66. — Through the heart further back. 



Fig. 67. — Through the fourth pair of mesoblastic somites, showing the ali- 

 mentary canal widely open below and the vitelline veins on each side. 

 Fig. 68. — Through the sixth pair of mesoblastic somites. 

 Fig. 69. — Through the twelfth pair of mesoblastic somites. 

 Fig. 70. — Through the ventral opening of the neurenteric canal. 

 Fig. 71. — Through the primitive streak. 



Fig. 72. — Through the pleuro-peritoneal cavity behind the embryo, to show 

 the posterior amniotic canal (P. A. C.) lying in the thickness of the 

 serous envelope. 

 Fig. 73. — Part of the last section more highly magnified, to show the pos- 

 terior amniotic canal lying in the serous envelope. 



Figs. 74—82. Stage K. 



Fig. 74. — Embryo 39, seen from above as an opaque object in spirit, with 

 the foetal membranes torn away from the front half, x 10. 



Fig. 75. — Embryo 39, seen from below, as before. X 10. 



Figs. 76 — 82. — Transverse sections of embryo 39, arranged in order ; drawn 

 under Zeiss A, ocular 1. 



