PLATE 7 



EXPLANATION OF FIGURES 



89 Ventral view of embryo, showing the curvature in a ventral direction; 

 the trochal disc is completely formed, but is very irregular; the ventral view 

 at this stage corresponds to the ends of the embryo. 



90 Longitudinal section of embryo represented in figure 89. 



91 and 92 Embryos, ventral view showing the overlapping of ends; the foot 

 at this stage is forked. 



93 Embryo showing maximum curvature. 



94 Embryo contracted into spherical condition. 



95 Longitudinal section of figure 93 taken to the side of the median line. 



96 A median longitudinal section of embryo passing through the brain region ; 

 note the position of the mouth; the embryo has begun to straighten. 



97 Embryo from left side, showing maximum development of foot; the seg- 

 mented appearance is due to the folded condition of the ectoderm. 



98 Longitudinal section of figure 97; the digestive system is completely 

 formed. 



99 Embryo showing the further separation of the two ends and the shortening 

 of the foot; the ciliated trochal disc is formed. 



100 An optical horizontal section passing through the floor of the pharynx 

 and the reproductive organs; note condition of body cavity and body wall. 



101 Median longitudinal section of embryo later than preceding; the mouth 

 has reached its definitive position at the ventro-anterior end. 



102 and 103 Horizontal sections of preceding figure through dorsal and 

 ventral sides, respectively. 



104 An optical section of embryo at time of birth, showing the relative 

 position and relation of difTerent organs. 



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