596 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [140] 



EXPLANATION OF PLATE X. 



Fig. 42. Embryo cod twenty-one days after impregnation, one day out of the egg, 

 seen from below. The positions of the sensory elevations sh are indi- 

 cated at the sides of the tail. The inner hypoblastic covering of the 

 yelk hy and the outer epiblastic covering ej) are shown in optic section, 

 with a space between them all around — the remains of the segmentation 

 cavity. The position of the mouth m is indicated as well as that of the 

 gill arches g 1. The heart, seen from below, is bent upon itself, and the 

 course of the intestine i is somewhat asymmetrical. The vent lies just 

 below the allantoic sac. The stellate pigment cells have aggregated 

 in two patches behind the vent on both the ventral and dorsal sides of 

 the tail, x 45. 



Fig. 43. One of the lateral sensory elevations of the preceding specimen in section 

 showing the nerve filament vf, which joins it to the spinal cord. The 

 elevation itself is seen to be only a thickened portion of the epiblast ep, 

 surmounted by sensory filaments sp. The relations of the muscle plates 

 pv, the chorda ch, and its sheath chs are also shown, x 120. 



Fig. 44. Germinal disk in the condition of the first cleavage of cod's egg four hours 

 old. X ■.\2. 



