SIGNIFICATION OF LETTERS IN PLATES. 181 



Signification of Letters in Plates I.-IX. 



Ch Notoehord. 



dm Yitelline membrane. 



Div) Anterior diverticula of 

 div / the alimentary canal. 



dv.r right diverticulum of the 

 alimentary canal. 



dv.l left diverticulum of the 

 alimentary canal. 



Dr Club-shaped gland, or its 

 foundation. 



Em Embryo. 



Ect Epiblast. 



En Hypoblast. 



En H Hypoblast cavity = Prim- 

 itive alimentary canal 

 cavity. 



FH Segmentation cavity. 



G M Gastrula-mouth. 



J Alimentary canal. 



K First gill-slit. 



Mes Mesoblast. 



MF Undifferentiated meso- 

 blast fold. 



MP Polar mesoblast cells. 



M E, Neural canal. 



Msc Muscle fibres. 



N Neural canal, neural plate. 



NF Fibre strand of the ali- 

 mentary carral. 



O Mouth. 



Oa Anterior opening of the 

 neural canal. 



pig Pigment spot. 



B, Polar bod\-. 



U S Mesoblastic somite. 



I. US, II. US First mesoblastic 

 somite, second meso- 

 blastic somite. 



V Vessel. 



v Edge of the layer growing 

 over the neural plate. 



Butler & Tanner, The Selwood Printing Works, Frome, and London. 



