Not being restricted to investigations on mammals, Bo j anus 

 performed his basic conclusions also on reptile embryos, mainly 

 on the adder (Coluber berus , or , according to the present 

 systematic terminology, Vipera berus L.}. Eramert confirmed 

 that in the reptile embryo the yolk duct is not present, i.e. 

 the duct connecting the yolk sac with the intestine. 



Concluding from the comparative embryological work, 

 Bo j anus doubted that this observation was correct; his 

 investigations led to other conclusions. The main part of 

 his work consists of thorough drawings with detailed 

 explanations. 10 The articles are summarized in the following: 



1) In the fetus of Coluber berus there is a yolk duct; 



2) this yolk duct is connected with the intestinal canal 

 not far from the origin of the appendix, i.e. it has 

 the same topographic relationship as the horse embryo; 



3) the yolk-mesentery vessels are situated primarily as 

 in other animals. 



Of the illustrations accompanying this work, Figure 21 

 is particularly remarkable. It shows the connection of the 

 yolk duct with the intestine at the early stage of intestinal 

 development when parts of the intestinal canal are still 

 undifferentiated. The yolk duct enters a region between the 

 stomach and the beginning of the intestine. Also shown is 

 that connection of the yolk-mesentery artery with the 

 descending aorta and the yolk-mesentery vein with the flooding 

 vein. 



This short account of Bojanus' embryological investiga- 

 tions confirms that he succeeded in settling a number of 

 important questions about the structure and reciprocal 

 situation of the embryonic membranes and embryonic organs in 

 mammals and reptiles. The results of his distinct investiga- 

 tions led him to argument with known authors of that time, 

 especially with Cuvier. Only later was it determined that 

 Bojanus 1 descriptions and discussions were much closer to the 

 truth. 



10. Bojanus, "Dottergang im Foetus des Coluber berus," ISIS 

 CI 818), pp. 2093 - 2094. 



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