THE MACKEREL FAMILY. 163 



but Holt shows that it is really situated at the vegetative pole 

 exactly opposite the middle of the embryo and that it gradually 

 migrates posteriorly as development proceeds. He also remarks 

 upon the 'cloudy' appearance of the globule. The period of 

 hatching extended over six days, with a mean temperature of 

 14'5°C. (Cunningham). 



The yolk is large and elongated and the head of the embryo 

 is closely pressed upon it ; there is no trace of a mouth. The 

 pectoral fins may be noticed as small semicircular folds far 

 behind the head. The vent opens a little way behind the 

 yolk-sac. The notochord is multicolumnar. The marginal fins 

 are broad and devoid of all pigment. Yellow pigment is found 

 upon the oil-globule and behind the eyes, black pigment also 

 occurs upon the oil-globule. Stellate black chromatophores 

 cover the dorsal surface of the head and trunk, with a tendency 

 to the formation of a median dorsal row. A few black dots are 

 also seen .ventrally. Holt notes that the chromatophores are 

 ' blue-black' and not ' dead-black' as in the rocklings. 



The oil-globule, although at first loose in the yolk, early 

 becomes fixed in position by the growth round it of a layer of 

 protoplasm. It may now be seen anterior to the hind end of the 

 embryo. At this stage (5th day) bright green pigment in 

 patches occurs, first behind the eyes and on the tail, near the 

 oil-globule. This pigment and the absence of all yellow colour 

 would at once distinguish the species from any of the gadoids 

 or pleuronectids. Holt described the pigment as of a yellow 

 colour by reflected light, and in a later paper Cunningham 

 explained the 'green' appearance as being due to the admixture 

 of black and yellow chromatophores. This is not a surprising 

 result when we recollect that Holt has noted that the black 

 pigment in this species is of a ' blue-black' tint. The green 

 appearance does not lose diagnostic value on account of its 

 being only an effect and not due to the presence of actual green 

 pigment. By transmitted light Holt found that the yellow pig- 

 ment appeared to be reddish-brown. 



In Plate VII, fig. 1 is shown a lateral view of the newly 

 hatched larva; 3'5 — 3'9mm. (Holt), 4'23 mm. (Cunningham). 



In four to six days the larva has grown to 4'16 mm. 



11—2 



