8 DR ARTHUR T. MASTERMAN ON THE 



In both figures the change in inclination of the mandible can be seen, the distance 

 from the eye to the tip of the snout becoming proportionally greater. The swim- 

 bladder has become oval in shape, and the notochord is less bent in its course dorsally 

 to it. A stage closely similar to this (fig. 6) is figured and described elsewhere,* from 

 which it appears that in the living condition there are numerous yellow chromatophores 

 intermingled with the black, giving the animal a greenish translucence. 



Fig. 7 shows great progress in the acquisition of adult characters, though little 

 growth in length has been effected (11 mm.). At about 9 mm., or the length of fig. 6, 

 the surface-water is forsaken and the progress through the midwater is gradually 

 effected. This alteration in habitat may be correlated with the striking difference in 

 structure. The caudal fin is now fully developed, the tip of the notochord, now no 

 longer median, being deflected upwards. 



The whole head is cod-like, and the angle of the lower jaw is at about 45° to the 

 perpendicular. A minute trace of the barbel has appeared, and a dense mass of black 

 pigment covers the brain. The dorsal and ventral lines have moved slightly from the 

 median line and are now clearly paired, and the former reaches to the head. The 

 lateral line is sharply defined. From the vent forwards the ventral line is small and 

 median. Patches of pigment cover the jaws and snout. 



All the adult fins are well differentiated, though still more or less continuous. As 

 has already been pointed out, the fin rays of the first dorsal are later in appearance than 

 those of the others. A cleared specimen shows the abdominal masses and the supra- 

 neural line of the internal pigmentation. 



A whole series of specimens carry us on to the stage in fig. 8, with a length of 19 

 mm. It will at once be seen that the changes in external structures effected from 9 mm. 

 to 11 mm. are considerably more marked than those which have taken place in the 

 growth from 1 1 mm. to 1 9 mm. Beyond the appearance of teeth, the further reduction 

 of the tip of the notochord, the further development of the first dorsal and the ventral 

 fins, there is little to note. The characteristic external pigmentation is still preserved 

 in all its details. The lateral pigment line reaches to the level of the middle of the 

 second dorsal. 



A specimen of -ff inch described by Prof. M'Intosh appears to agree very closely 

 with the usually occurring stages from this specimen (fig. 8) up to about 22 mm., whilst 

 these can easily be followed up through intermediate forms to fig. 9, in which the young 

 cod has reached 24 mm. in length (spirit). This would probably be little short of one 

 inch long in the fresh state. The head is now unmistakably that of a cod, and whilst 

 it is to be noted that the arrangement of the external pigmentation is still very 

 constant, apart from the fact that the mid ventral line from throat to anus is no longer 

 distinguishable, the proportions have changed. The angle of the jaw has receded to 

 well under the eye, and the ventrals have moved forwards. The young fish has at this 



* Loc. cit., pi. xix. fig. 2. 



