FOWL— SECOND DAY 



529 



the total length of the embryo such as that represented in Fig. 234a. 

 The blastoderm some little distance away from the median line of the 

 embryo is seen to consist of the usual two double layers — the somato- 

 pleure (som) composed of ectoderm and somatic mesoderm and the 

 splanchnopleure (spl) composed of splanchnic mesoderm and endo- 



Pio. 233.— Blastoderm and embryo Fowl with 18 mesoderm segments. 



a.e backgrowing edge of amniotic hood ; a.p, pellucid area ; a. l\ vascular area ; B, heart ; 

 ot, otocyst ; set, sero-amniotic connexion. 



derm. In immediate contact with the lower surface of the endoderm 

 in the complete egg there would be the yolk. In the splanchnic 

 mesoderm overlying the endoderm are seen the blood-vessels of the 

 vascular area. When traced inwards towards the mesial plane the two 

 layers of mesoderm are seen to come together to form the narrow proto- 

 vertebral stalk or nephrotome which joins up the lateral mesoderm to 

 VOL. II ^ M 



