330 



THE EVOLUTION OF MAX. 



and the four-layered stages). 3. The axial soldering, or 

 the coalescence of the germ-layers along the longitudinal 

 axis (giving rise to the axis-band). 4. The early sepa- 

 ration of the medullary tube from the skin-sensory layer 

 (by the formation of the dorsal furrow and the spinal 

 swellings). 5. The early origin of the primitive kidney 

 ducts (probably from the skin-sensory layer). 6. The early 

 division of the skin-fibrous layer into the chorda, the primi- 

 tive vertebral cords, and the trunk-muscle plates. 7. The 

 separation of the skin-fibrous layer from the intestinal- 

 fibrous layer (giving rise to the body-cavity, or ccdoma). 

 8. The rudimentary primitive vessels, or aortse (from the 

 intestinal-fibrous layer). These important germ-processes 

 result in the formation of ten different parts of the body, 

 which we may call " the primitive organs," and which, in 

 the following list, are represented in their relation to the 

 germ-layers. (Cf. Fig. 99, and Plate IV. Fig. 3.) 



