178 ON THE COMMON WHITING OF MOKETON BAY 



membrane near the tail. Yellow cells show along the sides of 

 the body. The wrinklings are now much diminished. At 

 12|hrs. (fig. 12), the embryo shows the optic lobes, notochord 

 and Kuppfer's vesicle. At 14^hrs., Kuppfer's vesicle begins to 

 be narrowed, and distinctly pointed towards the capsule as the 

 tail elongates. Then it gets ainaller, and appears to retreat from 

 its position at the tip of the tail, and ultimately disappears after 

 having existed for about 3 hours. Fig. 13 shows the optic lobes 

 cut off, and the appearance of the muscle flakes on the body. 

 At this stage, the rounded ends of the myomeres give a crenated 

 appearance to the sides of the body. At 17^ hours, the heart 

 shows as an aggregation of cells on the breast, and an hour 

 later is beating faintly. In fig. 14 at 19 hours, the optic 

 vesicles have been invaginated, and the tail is slewed to one 

 side of the oil drop. Fig. 15 is a side view of the stage shown 

 in fig. 14. The heart (ht.) in a capsule under the chin, is a tube 

 extending from the median line to the left and forward. The 

 choroidal fissure of the eye is seen. Fig. 16, 22 hours, shows 

 the otocyst and a membrane enveloping the oil globule. Just 

 before hatching, a part of the continuous fin shows on the tail. 

 The eggs from which the series of drawings so far were taken 

 hatched at 23^ hours from time of extrusion. The temperature 

 of the water ranged from 25-6" to 27" C. 



The larvae figured on Plates X. and XL, were hatched in 

 colder weather — temperature 22° to 23*^ C. The stage shown in 

 fig. 17, occurred at 38 hours after extrusion. The continuous 

 fin (c.f.) is well developed, and the vent and the urinary vesicle 

 behind it are seen. The yellow pigment has taken its character- 

 istic early larval arrangement. In figs. 18 and 19 the gut is 

 shown forming and stretching forward to the yolk, while a few 

 finely branching pigment cells show on the membrane enclosing 

 the yolk. At 70 hours the pectoral fins make their appearance 

 (fig. 20). The membrane enclosing the yolk, which has up to 

 this stage maintained its position, as the yolk and oil globule 

 diminished in size, now suddenly collapses, and the yolk moves 

 forward. While the membrane remain d turgid it interfered 

 with the locomotion of the larva, which was forced to swim in 

 circles, but from this onward the young fish swims actively. 

 Soon after hatching when the larva is floating passively, the 

 position is horizontal and supine. From the stage shown at 

 fig. 19, the position is vertical with the tail upmost. 



