Embryologic Development of Animals 449 



Neuraf plat? 



Neuraf groove 



Notochot-d 



Mesoderm 



Endoderm 



Neural tube 



1 Notochord 



Mesoderm 



Somatic 

 mesoderm 



a Ectoderm Endoderm i Ectoderm ^"docJerm 



Spinal cord 



Notochord *'*^''te 



,/ \ 



Notochord ^ 



tctoderm 



Splanchnic ^ 

 mesoderm / 



Spinal cord 

 Vertebra ' Dorsal root 



■» ' OandJinn 



i Sanglion 



Genital 

 ridge 



f ndflderm d 

 Brain 



Muscle 

 segment 



^Primitive 

 kidney 



^■^Mesenchyma- 



Coeion 



Digestive 



Ectoderm (Body cavity) "" tf^ct 



<^n;K,.,i ,-r..A Notochord Neurenteric 



t)pinal|COrd > canal 



Anal pit 



Digestive tract 



smaA 



Liver 

 outgrowth 



Coelonr* 

 (Body cavity) 



Fig. 222. — Development of a vertebrate, shown somewhat diagrammatically. 

 Stages a-e are cross section of mid-body region, a. Neural plate stage; b, neural 

 groove stage; c, neural tube stage; d, spinal cord stage; e, spinal cord stage still 

 later; f, embryo cut lengthwise to show internal structures. (From Being Well 

 Born, by Michael F. Guyer. Copyright 1927. Used by special permission of the 

 publishers, The Bobbs-Merrill Company.) 



