458 



DEVELOPMENT OF PRIMITIVE BODY FORM 



NEURAL ECTODERM 



PIDERMAL 

 ECTODERM 



SU8N0T0CH 



EPIDERMAL 



ECTODERM 



ENTODERM 

 NEURAL TUBE 



PERIBLAST 



COELOM 



VENTRO-LATERAL 

 MUSCLE TRACT 

 WOLFFIAN DUCT 



ECTODERM 



EPIDERMAL ECTODERM 

 MESODERM 



NOTOCHORD 



ENTODERM 



Fig. 218. Solid keel of neural ectoderm in teleost and bony ganoid fishes. (A and B 

 after H. V. Wilson, 1889; C after Dean, 1896.) (A) Neural ectoderm separating from 

 epidermal ectoderm. (B) Neural tube completely separated from epidermal ectoderm. 

 (C) Late gastrular condition of Amia calva. 



of the respective body tubes tends to follow a similar procedural plan through- 

 out the entire vertebrate series. 



2. Common, Vertebrate, Embryonic Body Form 



As a result of the changes outlined above and the tendency to form common, 

 generalized, structural conditions during the early phases of development, a 

 common, generalized, primitive embryonic body form is developed in the 

 embryos of all vertebrate species in which the rudiments of various, future, 



