delicate semitransparent bodies almost cylindrical in form, 

 terminating in very thin vacuoles. Between the heart and 

 the lungs, below the auricles, the right lobe of the liver 

 is situated, continuing with convex peritoneal and concave 

 dorsal surfaces which are adjacent to the heart; the portal 

 vein goes through this lobe. The left lobe of the liver is 

 narrow; it is located near the stomach and the duodenum. 

 The kidneys are very long, with a lobed structure. They 

 start at the chest region near the lungs and extend along 

 the posterior end of the colon, to which they are connected 

 to the urinary canal. Legs and wings appear as distinct 

 hillocks. On the development of the mandibles, Pander 

 referred to Tredern's observations. The cavity of the 

 chorion as Pander called it, increases in size. In a foot- 

 note, Pander mentions the controversy about this organ and 

 refers to Haller's unsuccessful attempts to blow air into 

 the allantois through the intestines, or vice versa. 

 Tiedemann gave more accurate data about the allantois, and 

 Pander quoted him: "This sac is hung on a stem which 

 is rich in vessels including both, the umbilical arter- 

 ies. The sac is composed of two layers — the external 

 layer which is rich in vessels, and the internal 

 which is thin and without vessels, containing transparent 

 fluid. The cavity of the sac, through a canal extending 

 between the umbilical arteries, connects with the terminal 

 part of the colon or the cloaca .... The external layer 

 of the sac is analogous to the vascular layer (chorion), 

 and the internal layer could correspond to the allantois." 



The last paragraph of the dissertation (§ 13) is 

 concerned with the condition of the chick embryo at the 

 fifth day of incubation. The yolk membrane has disappeared. 

 The false amnion, i.e. the serous membrane in Baer's terms, 

 becomes adjacent to the shell membrane. The true amnion 

 is completely closed. The spreading chorion is connected 

 internally with the false amnion. The descending and 

 ascending veins of the vascular area are in the process 

 of disappearing. The middle intestine is almost closed. 

 Between the intestinal layers, there remains only "a small 

 yolk intestinal canal connecting the intestine with the 

 yolk. The serous and mucous layers are entirely separated 

 from each other, the first of which . . . above the back 

 forms the amniotic membrane; the latter together with the 

 mucous layer include the yolk." Pander considered neural 



259 



