76 



GENERAL SKETCH OF 



The heart is formed of a solid and rounded projection of 

 the middle layer bulging out towards the subjacent periblast. 



20th April, 6th day. The brain is now differentiated into 

 fore-brain, mid- and hind-brain (Figs. 25 and 26). The lens 



Fig. 25. Egg of Cod with embryo 

 on 6th day. Lateral view. 



Fig. 26. Egg of Cod with more 

 advanced embryo on 6th day. 

 Ventral view. 



of each eye is complete, and otoliths have appeared in the 

 otocysts. The heart assumes a conical tubular appearance, and 

 the inner layer (hypoblast) has formed the gut, in which a 

 cavity is now apparent — large in the median region, and 

 tapering to the solid anterior part. The liver appears as a blind 

 diverticulum of the gut, on the right side in most views. 

 The otocysts are more ovoid in shape, and the notochord 

 reaches forward to them. It has a downward flexure at 

 its anterior end and shows signs of vacuolation. The third 

 pair of sense organs, or nasal pits, is now indicated. Three 

 diverging lines on the ventral surface of the brain indicate the 

 lateral ventricles. 



The pectoral fins are outlined, and delicate protoplasmic 



Fig. 27. Egg of Cod with embryo 

 on 9th day. Nearly dorsal view. 



Pig. 28. Egg of Cod with embryo 

 on 9th day. Lateral view. 



