The Development of the Alligator 313 



plate, along whose medial side it courses. The 

 ventral nerve root is plainly seen; the dorsal root, 

 in this section, less plainly. The amnion (a) and 

 abdominal wall are, as in the preceding figure, 

 torn in the region of the ventricle. 



Figure 17 'e is a short distance posterior to the 

 figure just described. The liver is cut through its 

 middle region and forms a large, darkly staining, 

 reticular mass on the left side of the figure. The 

 digestive tract is seen at two places to the right of 

 the liver; the smaller and more ventral of these 

 openings (i) may be called the intestine, while 

 the larger is evidently the stomach (i 1 ). The 

 body wall is here unfused and becomes suddenly 

 thinner as it passes upward into the amnion (a). 

 The Wolffian tubules (wt) form a very conspicuous 

 mass on either side of the mesentery, in close con- 

 nection with the posterior cardinal veins (pc). 

 In the mesoblast between the dorsal aorta (ao) 

 and the notochord are two small, irregular, darkly 

 stained masses (sy). These are shown in the 

 preceding two figures, but were not mentioned 

 in the description. They may be traced through 

 a great part of the length of the embryo back of 

 the head region; at intervals corresponding in 

 length to the distance between the spinal ganglia 

 they are enlarged, while between these enlarge- 

 ments they are very small in cross-section. At 

 certain points a small blood-vessel is given off by 

 the dorsal aorta to the immediate neighborhood 



