594 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [138] 



EXPLANATION OF PLATE IX. 



Fig. 35. Germinal disk of cod's egg four hours old. 



Fig. 36. A similar disk in an abnormal condition. 



Fig. 37. Another abnormal form. 



Fig. 38. Germinal disk of cod's egg past the second cleavage, and consisting of four 

 cells ; an abnormal form. 



Fig. 39. A similar disk six and a half hours old, normally developed. All of the five 

 preceding figures are magnified thirty-two times. 



Fig. 40. Embryo cod twenty-two days after impregnation, which has escaped from 

 the egg twenty -four hours since, seen from the side. The gill clefts now 

 show distinctly as parallel furrows which have barely just broken through 

 behind and below the eye. The heart has also been differentiated into its 

 four principal divisions, and the venous sinus has its mouth directed 

 upwards and backwards. The brain is relatively shorter and deeper, 

 and the position of the future mouth is indicated at m. The allautois 

 al is now clearly visible as a large vesicie above the vent v. The liver 

 Iv has been still further differentiated, together with the air bladder y. 

 Lateral seusory elevations, which are connected by a nervous thread to 

 the spinal cord, surmounted by fine hairs, have apjteared in the epiblast 

 or epithelium ot the young fish at sh, sh. The breast fin bf is now nearly 

 circular in outline, but its base still has a longitudinal direction, x iO. 



Fig. 41, Heart of the above, more enlarged, showing its cellular structure aud vts 

 four principal chambers, x 100. 



