GERM-LAYER THEORY 



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Pronephros), the kidneys, the sex glands, and the series of 

 " blood-glands" suprarenals, thyroid, thymus and spleen. 

 Baer did not attach any special morphological significance to 

 the peritoneal lining of the body cavity, as is done in more 

 modern forms of the germ-layer theory. The gill-slits were 

 largely formed by outgrowths from the alimentary canal. 



In his germ-layer theory von Baer was influenced a good 

 deal by Pander, to whom the actual discovery of the process 



FlG. 7. Ideal Transverse Section of a Vertebiate Embryo. 

 (After von Baer.) 



a. Chorda. 



b. Dorsal plates. 



c. Ventral plates. 



d. Spiual cord. 



e. Vessel-layer. 

 /. Alimentary tube. 

 g. Pronephros. 

 h. Skin. 



i. Amnion. 



k. Serous membrane. 



I. Yolk-sac. 



of layer-formation is due. Pander, however, had distinguished 

 only three germ-layers, an upper " serous " layer, a lower 

 " mucous " layer and a middle " vessel-layer." He it was who 

 introduced. the terms " Keimhaut " (blastoderm) and " Keim- 

 blatt " (germ-layer). 



The honour of being the founder of the germ-layer theory 

 is sometimes attributed to C. F. Wolff, notably by Kolliker 

 and O. Hertwig. Wolff, it is true, in his memoir Deformatione 

 intestinorum (1768-9) showed that the alimentary canal was 



