MUSEUM OF COMPATIATIVE ZOOLOGY. 103 



PLATE XII. 



Fig. 74. Sagittal section (left-hand surface) from an embryo somewhat older than 

 the preceding. 



" 75. Sagittal section of the lungs at about the time of hatching. 



" 76. Sagittal section of the lungs five or six days after hatching ; the upper 

 and lower walls of each lamella are connected by the union of the 

 nuclei (n/.). 



" 77. Sagittal section showing the nervous system at the beginning of reversion. 



" 78. Sagittal section of the cephalothorax at the time of hatching, to show the 

 post-stomodaeal portion of the alimentary canal, and also the concen- 

 trated condition of the ventral ganglionic mass. 



