Normal Plates of the Development of Necturus maculosus. ■il 



Hypophysis. 



In the 9 mm embryo, series lo6, 107, the anla<i^e of the hypophysis is two layers of cells thick, in 

 108 it is but a single layer, while in 109 it is three or four layers thick. 



Liver. 



In the 9 mm embryo, series 106, 107, 108, 110 tlie anläge of the liver is shown as a wide evagination 

 of the gut; while 109 shows two or three tubules. 



Pancreas. 



The dorsal pancreas seems to grow very slowly and to show much Variation. Series 118 and 119 

 show the dorsal pancreas as a slight evagination of the dorsal wall of the gut. In series 120 it is in 

 about the same stage. In series 125 the evagination is vesicular. In the 13 mm embryo series I2I, 

 there is a cup-shaped evagination. In 122, 124 the evagination is vesicular. In the 14 mm stage it varies 

 from cup-shaped evagination in series 127, 130 to vesicular in 129. 



Spleen. 



In the 15 mm embryo, series 131, 134 show the anläge of the spieen as a small mass of mesenchymal 

 cells in the dorsal mesentery of stomach. In series 132 there is no indication of spieen. In 133 there is a 

 well defined mass of mesenchymal cells. 



Thymus. 



In the 16 mm embryo, series 137, 138, 139 the thymus begins as a small mass of cells in close 

 proximity to the 3rd branchial cleft. In 136 the thymus anläge is not yet present. 



Trachea — Lungs. 



In the 10 mm embryo series lll, II2 show the beginning of the trachea as a short groove in the 

 ventral wall of the pharynx. Series I13 shows a deeper vesicular evagination. 



