The Development of the AlHgator 299 



marked than is shown in the figure. On either 

 side of the spinal cord a large spinal ganglion (sg) 

 is seen, closely wedged in between the spinal cord 

 and the adjacent muscle plate (mp). As in the 

 preceding stage, there is a marked space between 

 the muscle plate and the adjacent ectoderm (ec). 

 The somatic mesoblast at the upper angle of the 

 unenclosed body cavity is thickened on each side 

 and somewhat bulged out by the Wolffian body to 

 form what might be termed a Wolffian ridge (wr) . 

 In the mid-ventral line is the considerably de- 

 veloped mesentery (ms) , from which the intestine 

 has been torn. The Wolffian bodies now consist, 

 on each side, of a group of five or six tubules (wt) of 

 various sizes, near which in a more ventro-lateral 

 position, close to the upper angle of the body 

 cavity, is the more distinct Wolffian duct (wd). 

 The allantois is fairly large by this time, and may 

 be seen in the most posterior sections as an irregu- 

 lar, thick-walled outgrowth from the hindgut. 



A horizontal section through the anterior end 

 of an embryo of this age is shown in Figure 15/. 

 While enclosed of course in the same membranous 

 amnion (a), the pharyngeal region of the section 

 is separated by a considerable space from the 

 more anterior region where the section passes 

 through the forebrain (fb) and eyes. The spinal 

 cord (sc), notochord {?jf), muscle plates (mp), aortae 

 (ao), and anterior cardinal veins (ac) need no spe- 

 cial description. The appearance of the pharynx 



