Contents. 



page 



Introduction l 



General Sketch of the Course of Development in Lepidosiren and Protoptnrtis ... 2 



External features 2 



The skin 3 



Nervous System 3 



Peripheral nerves 4 



Olfactory organ 4 



Eye 4 



Otocyst 5 



Skin sense organs 5 



PiNKUs' Organ 5 



Pituitary body 5 



Alimentary canal 5 



Buccal cavity 5 



Visceral clefts r 6 



Lung 6 



Thyroid and thymus 6 



Digestive tract 7 



Liver 7 



Pancreas 7 



Coelomic organs 7 



Splanchnocoele 8 



Myotomes 8 



Nephridial System 8 



Archinephric ducts 9 



Mesonephros lO 



Genital ducts lO 



Gonads lo 



Organs of the mesenchyme n 



Skeleton ii 



Tables 12 



Conclusion 20 



Literature 27 



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