50 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



they show no connection with the central nervous system, these 

 structures appear to be the rudiments of the sympathetic nerves. 



Figure 17/ is in the region just in front of the hind legs. The 

 abdominal walls are here unfused, and into the unenclosed body 

 cavity projects the intestine (*), supported by a narrow mesentery 

 and surrounded by a comparatively thick mass of mesoblast. The 

 Wolffian body and duct form a mass of considerable size on each 

 side of the mesentery. The Wolffian body is cut near its posterior 

 end and consists of smaller tubules than in the more anterior regions. 

 The Wolffian ducts (wd), on the other hand, are very large and are 

 much more clearly distinguishable from the Wolffian tubules than 

 in the preceding sections. The Wolffian ridges (wr) are very 

 marked projections on the sides of the body, and in a region further 

 caudad become especially developed as the posterior appendages, to 

 be described in connection with the following section. Both spinal 

 ganglia are shown in this figure (sg), and in connection with the 

 left ganglion the spinal nerve (sn), extending ventrally as far as 

 the level of the Wolffian duct. The sympathetic nerve rudiments do 

 not extend so far caudad as the plane of this section. The dorsal 

 end of each muscle plate (»ip) is seen, in this and other sections, to 

 be slightly enlarged to form a round knob ; this knob contains a dis- 

 tinct cavity ( not shown in the figure) , the myocoel. 



In figure ijg, owing to the curvature of the body, the plane of 

 the section passes through the body at three places : through the 

 region of the heart and lungs (fig. 17c?), through the region of the 

 posterior appendages, and through the tail. In fact, the plane of the 

 section represented by each of the preceding figures cut the embryo 

 in more than one region, but for the sake of simplicity only one 

 region was represented in each figure. In the figure under discus- 

 sion only the leg and tail regions have been drawn, though the latter 

 region (t), being cut through one of its curves, is seen as an elon- 

 gated body with a section of the spinal cord, notochord, etc., at each 

 end. Both regions shown in the figure are enclosed in the same fold 

 (a) of the amnion. Of the structures in the dorsal side of the larger 

 or more anterior part of this figure nothing need be said. The most 

 striking feature of the section is the presence of the large posterior 

 leg rudiments (pa). As was noted in the preceding figure, they are, 

 as usual, merely local enlargements or projections of the mesoblast 

 (covered, of course, with ectoblast) of the Wolffian ridge. They 

 are, as shown in this section and in the surface view of this stage 

 (fig. 17), bluntly pointed projections from the sides of the body. 

 The anterior appendage seems to be slightly more developed than 

 the posterior, as was noted in describing the surface view of the 



