DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 887 



the 1st of May the upper arch of the cranial cavity, and a considerable portion of the sides 

 superiorly, are covered with continuous pigment. It extends along the spinal cord — en- 

 veloping two-thirds of its surface dorsally — while the lower aspect is free from it. The 

 abdominal cavity has a continuous coating on its silvery peritoneal surface, and the same 

 occurs, as previously noted, round the segmental organs. A dense layer of pigment also 

 lies beneath the skin, over the muscles, and posteriorly the upper arch splits to send off a 

 layer to the tip of the interspinous bones. The latter layer ceases a little above the bases 

 of the V-shaped fin-rays. There is considerable variation in the pigment, some specimens 

 towards the end of June, with the yolk-mass completely absorbed, presenting in trans- 

 verse section, besides the continuous layers, large isolated pigment-masses here and there, 

 breaking the continuity of the layer, both in the subcutaneous and peri-nervous regions. 



The silvery sheen extends a short distance over the yolk-sac. The dorsum of the 

 head is deeply pigmented, while the sides are less so. A little below, the lobes of the 

 brain are outlined by their blackish pigment. About the middle of May, the con- 

 dition of the young fish is shown in the figure before mentioned (PL XXVII. fig. 1). The 

 pigment on the dorsum and sides is dull blackish or a uniform dull grey, with black specks. 

 The abdomen is silvery and iridescent, as well as dotted with black pigment-corpuscles. The 

 pectorals have a little pigment at their bases, and the same is present along the bases of 

 both dorsal and ventral marginal fins, the former being definitely banded. The tail is still 

 translucent. The iris is iridescent silvery, with black pigment — chiefly visible superiorly. 



When about five inches in length, the dorsal fin has about a dozen black spots at inter- 

 vals, the anterior being nearer the free edge than the posterior. The sides are also marked 

 by a somewhat reticulated arrangement of spots which, in a few instances, coalesce to form 

 bars. The lateral dark patches proceed from those in the dorsal fin, and meet when about 

 a third of the body is traversed, and then they form a single or double band to the ventral 

 border, which is devoid of them. The increase in the pigment, e.g., at six inches, demon- 

 strates how, from the former arrangement, the bold stripes on the sides and dorsal fin of 

 the adult are formed. The hue of the latter must render it very much in harmony with 

 its surroundings on rough hard ground amidst stones and zoophytes. 



In the young salmon we find many points of contrast at this stage. The pigment 

 on the head is much developed on extrusion from the egg. A few black pigment- 

 corpuscles occur beneath the cranial tract and along the spinal cord, but they are 

 isolated, and often in the abdominal roof only a single one occurs in a transverse section 

 of the fish. In this region, also, a line of pigment passes dorsally on each side of the 

 median (embryonic) fin. A few, again, occur at the base of the ventral median fin. Both 

 cease before reaching the tail. The young salmon at this period is of a translucent pale 

 yellowish hue, with a tinge of pink, while a considerable number of pigment-corpuscles 

 are present on the head, and a chain of them along the neurochord. The large oil- 

 globule is of a dark orange-colour. The pigment very soon becomes denser at the upper 

 part of the yolk-sac, as well as over the body of the fish. The indications of the " parr- 

 'marks" occur at the third week. A little later (fourth or fifth week) the pigment 



