Plate V. 



Fig. 35. A median longitudinal section taken in the plane CR of Fig. XI. 

 See text for description, x 1^7. 



Fig. 36. Enlarged anterior end of the preceding, x 245. 



Fig. 37. Enlarged posterior end of Fig. 35. X 245. 



Fig. 38. From a section, four sections to the left of the one represented 

 in Fig. 35. The cavity in the thick dorsal lip is, perhaps, the remains of 

 the space that was formed between the upper and lower layers when the 

 former turned under to give rise to the latter, x 245. 



Fig. 39. From a section, two sections to the right of the one represented 

 in Fig. 35. It shows the same conditions as the preceding, x 245. 



Fig. 40. Posterior end of a section taken through KF of Fig. XI. The 

 tip end of the zone of junction («) is shown, and also the lateral portion 

 of the dorsal lip of the blastopore. X 245. 



Pig. 41. Posterior end of a section taken through OH of Fig XI. There 

 is no overhanging margin (dorsal lip) in this section, x 245. 



