The facial parts undergo the following changes. The 

 frontal projection between the olfactory depressions elongates. 

 The projections of the upper jaws grow, reaching the frontal 

 projection by the seventh day. Since the upper jaw projections 

 do not reach the end of the front projection, wide slits form 

 and connect from both sides with the mouth opening. The lower 

 jaw forms from the primary branchial arch, then becomes 

 enlarged and pointed at the end. The foundation of the tongue 

 appears . 



The esophagus becomes elongated; the gizzard is displaced 

 to the left; the glandular stomach is already marked separately, 

 but not sharply limited from the gizzard. The intestinal loop 

 sits behind the stomach (the duodenum). The next loop, the 

 beginning of the small intestine, enters the umbilicus. Part 

 of the small and the large intestine forms the last curve of 

 the intestine, or the whole remaining intestine. The respiratory 

 tube elongates; the lungs are completely distinguished from the 

 esophagus and are divided into anterior (larger) and posterior 

 divisions. The larynx appears in the place of the passage of 

 the respiratory tube into the throat . 



From each Wolff's body, Baer observed a sudden appearance 

 of a thickly walled canal, which passes along the Wolff's body 

 and parallels that canal in many fishes which extends from the 

 abdominal cavity to the sexual orifice. This canal, thin at 

 the anterior part, becomes lost somewhere near the auricle. Its 

 posterior end can be traced to the point where it falls into 

 the cloaca. Baer concluded from an error that the Wolff's body 

 forms the blood-carrying vessels. Observing on the seventh 

 day the presence of many ducts going from the Wolff's body 

 into the canal mentioned earlier, Baer stated the possibility 

 that this canal also represents a modified blood vessel. Since 

 the walls of this canal are very thick and its diameter is 

 large, Baer came to the conclusion that the described canal 

 represents a sexual duct. Baer did not resolve the contradic- 

 tions of the vascular origin of the Wolff's body with other 

 peculiarities. Thus he stated that "the method of forming 

 the Wolff's body remains so fer unclear"( I 9 q; p. 154 (98)). 



In this place, Baer's investigations reveal with great 

 clarity his thoroughness of observation, his carefulness in 

 conclusion, and his readiness to withdraw inaccurate conclusions. 



330 



