600 WILLIAM PATTEN. 



Fig. 10. — Lateral view of the embryo in about the middle of the fifth stage. 



Tig. 11. — Same embryo two days later. At p.*' ^' ^ may be seen the rudimen- 

 tary abdominal appendages ; a. sL, anal stylets in optical section. 



Fig. 12. — Lateral view of an embryo about twelve days old. The tip of 

 the abdomen is bent back as far as the eighth abdominal segment. 



Fig. 13. — Lateral view of the embryo in the latter part of the fifth stage. 

 The tip of the abdomen has reached the sixth abdominal segment. 



Fig. 14. — Embryo, just before the rupture of the embryonic membranes ; 

 ft., bodies, which in Blatta we have shown to be salts of urea, and which are 

 undoubtedly of the same nature here. 



Fig. 15. — Lateral view of the right side. Embryo in the last stages of 

 revolution, the membranes have ruptured and collected on the back to form 

 the dorsal organ, d. o. 



Fig. 16. — Lateral view of the embryo from the right side, after the com- 

 pletion of revolution. 



PLATE XXX VIb. 



Figs. 1, 2, and 3. — Three successive stages in the formation of the 

 " blastema." 



Fig. 4. — Longitudinal section through the egg in blastoderm stage. 



Fig. 5. — A similar section during the formation of the ventral plate. 

 a. Yolk-cells in the act of separating from the serosa. 



Fig. 6. — Section through a mesodermic segment, showing two cells in the 

 act of separating from the mesoderm and passing into the yolk. 



Fig. 7. — Longitudinal section of the ventral plate, showing another cell in 

 the act of separating from the mesoderm. 



Fig. 8. — Longitudinal section through the ventral plate, showing the forma, 

 tion of the embryonic membranes. At y. c. and .r. are two cells in different 

 stages of separation from the ventral plate and serosa. 



Fig. 9. — Cross section of ventral plate in head region, showing the gas- 

 trular invagination at ffst. 



Fig. ]0. — Section similar to that in Fig. 9, only in a later stage. The 

 embryonic membranes have united over the median line of the ventral plate. 

 The gastrular invagination has disappeared, leaving a group of median cells 

 behind. 



Fig. 11. — Cross section in thoracic region before the appendages have 

 appeared. The mesoderm has spread out into almost a single layer of cells, ms. 

 The gastrular groove has entirely disappeared. 



Fig. 12. — Cross section through the ventral plate during the early stages 

 of the nervous system. A few nuclei have appeared at the deep ends of the 

 ectoderm cells, on either side of the neural furrow. The mesoderm has 

 separated from the median line and is thickened at the outer margins. 



