Early Post-Larval Stage. 9 



The dorsal fin-ray is now very distinct. The pectoral fins have also grown con- 

 siderably, and are moved vigorously by the larva. 



The larva at this stage measures, in the living condition, about 5"5 mm. The 

 yolk is, however, much smaller in comparison to the total length of the larva, and the 

 pigment-free tail is also much larger than the diameter of the yolk. 



The larva has become much thicker and more opaque, although the body pig- 

 ment does not extend much behind the dorsal fin prominence. The tail is still 

 practically pigment-free, but in some larva? there may appear a single dendritic 

 pigment spot on the notochord near the middle of the tail, and there may also appear 

 the beginning of pigment on the ventral surface near the tip of the tail. Usually, 

 at this stage, the mauve pigment has disappeared from the gut. The dorsal fin 

 filament has now grown considerably in length. The pelvic fins are, however, 

 very striking objects. They arise from the surface of the yolk-sac as long conical 

 prominences posterior to the fan-shaped j^ectorals. As the yolk gets absorbed, 

 the pelvic fins grow rapidly in length, and gradually get shunted forward, until 

 finally at the complete absorption of the yolk they are inserted on the ventral 

 surface of the body anterior to the pectorals. Small pigment spots appear on the 

 tips of the pelvic fins, but the pectoral fins, as yet, are pigment-free. 



Soon after this stage, the larvae begin to lose their characteristic position at the 

 surface of the still water. They gradually sink towards the bottom of the vessel 

 and, although they may remain suspended in the water for some little time, they 

 finally come to rest on the bottom. No difficulty is encountered in rearing the 

 larvee in a hatchery until the absorption of the yolk. In the summer months, the 

 absorption of the yolk is completed in about fifteen days. 



Larva at the Completion of the Absorption of the Yolk. 



{Ficj. 5). 



A very fine specimen at this stage was caught in a bottom tow-net at 

 Station 36 (58° 26' N. ; 0° 8' W.) on the 15th July 1914. The larva, after pre- 

 servation in 2 per cent, formalin for a few days, measured 8 mm. It still retains 

 the characteristic form, and shows no signs of depression of the head or body. The 

 head is two-sevenths of the total length, and the notochord extends as a supporting 

 rod the whole length of the elongated tail. The embryonic fin is broad and still 

 quite complete. The head and body regions are now completely covered with pig- 

 ment, and this feature, together with the elongated, almost pigment-free tail, gives 

 to the larva its superficial tadpole-like appearance. The pigment on the head 

 and body is of a delicate dark brown colour, merging into black over the brain and 

 behind the pectoral fin. The eye is still normal in position, slightly nearer to the 

 tip of the snout than to the insertion of the pectoral fin. It is dark, with a bluish 

 shimmer. The mouth, at this stage, is well-formed and open, whilst the gill-cover 

 is also very distinct. 



The pectoral fins are large, transparent, and fan-shaped, the posterior border 

 extending almost to the anus. They are inserted on the body just half-way 

 between the posterior border of the eye and the anus, and have lost the distinctive 

 fleshy appearance of the early larval stages. They are only made out with diffi- 

 culty against the darkly pigmented body. 



The greatest changes have taken place in the dorsal fin-rays and in the pelvic 

 fins. A second dorsal fin-ray element has arisen behind the first ; it is shorter and 

 not so robust, but both rays end in a fine filament. The length of the first ray is 

 greater than the depth of the body. 



The pelvic fins have now entirely lost their primary form. They are shunted 

 very far forward, and are inserted on the ventral surface in front of the pectoral 

 fins. They have increased enormously in length, and are long, simple, filamentous 

 rays, pigmented at the tip. They extend to the mid-point of the total length of 

 the larva. 



In this specimen there is a single large chromatophore on the notochord in 

 the middle of the tail. As yet, there are no signs of the development of the unpaired 

 fins. 



There are no indications, up to this stage of development, that the larva belongs 



