The Frog Book 



bide Vi( 



F 



groove 



lolk 



Pl.ATK I.XV 



■Yolk 



Fig. 202.— April 9, iqo2. LEOPARD FROG'S EGG, greatly magnified. The upper portion is black; the lower in 

 cream-white. The first vertical partition is forming. [Providence, R. I.] 



Fig. 203. — Drawn to show first two vertical grooves corresponding to two partitions which divide the egg into four 

 cells. ( Egg tipped to show top. ) 



B 



.'Neural 



qroove 



Fig. 205.— The cells are too small to be seen. A dark line of crescent shape appears on one side of tlie egg. 



Fig. 206, A. — Morning of third day (April nth). Egg drawn from posterior end. All of the yolk except a mere 

 plug is covered by the dark living portion of the egg. 



B.— Afternoon of the third day. Egg as seen from left side. Volk-plug marks posterior end of embryo. Neural 

 groove forming along the back. 



Head 

 end 



Neural fold 



, Neural qroove 



Fig 207.— April 12th. Drawn from left side (as B. Fig. 206) but tipped to show back. The neural folds are closing 

 in over the neural groove to form the nerve tube The anterior of this will make the brain, the remainder will be the 



spinal cord. 



