DEVELOPMENT OF THE AMERICAN ALLIGATOR REESE 49 



the liver (//'), which has the appearance of a mass of darkly stained 

 cords or strands of cells surrounding- a large blood-vessel (in?'). 

 This blood-vessel may be ea.Ied the meatus venosus, though it is not 

 separated by any line of demarcation from the auricle. A few 

 sections anterior to this region the meatus venosus opens dorsally 

 into a large vessel on each side (dc) , which at first glance seems a 

 part of the body cavity, but which is in reality the ductus Cuvieri, 

 formed by the union of the anterior and posterior cardinal veins. 

 An irregular, crescentic cleft (be), lying medial and parallel to each 

 of the Cuvierian vessels, is the body cavity. In the upper angle of 

 this cavity is a granular mass, the glomerulus, that of the left side 

 being accompanied by the extreme anterior end of the Wolffian duct. 

 In the rounded mass of mesoblast, between the cleft-like regions 

 of the body cavity, the lung rudiments {lit) and the oesophagus (oe) 

 are seen as three small, circular openings ; that of the oesophagus is 

 somewhat smaller than the other two. The notochord (nt), spinal 

 cord (sc), and muscle plates (nip) have almost the same appear- 

 ance as in the preceding section. A spinal ganglion (sg) is seen on 

 each side of the spinal cord ; the one on the left shows a well-defined 

 spinal nerve (sit), which may be traced ventrally as far as the end 

 of the muscle 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 pre- 

 ceding figure, torn in the region of the ventricle. 



Figure ije is a short distance posterior to the figure just de- 

 scribed. 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 (/'). 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 enlargements 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 of each' of these small areas. Although 



4— A I. 



