DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 895 



mentioned. A further stage is shown in the coloured figure of the young fish about the 

 middle of May (PL XXVII. fig. 1). In this the upward direction of the dorsal border 

 of the tail is evident, but the organ is perhaps less elongated (antero-posteriorly) than 

 in the previous stage. 



The difference between the tail of the larval fish and that of the adult is obvious, 

 for in the latter it is somewhat dwarfed by the great development of the median fins — 

 dorsal and ventral — and its antero-posterior diameter is considerably less than the depth, 

 for instance, of the dorsal ; whereas, in the young stage, its long diameter much exceeds 

 the depth of the latter, and both the dorsal and the ventral diminish in front of it so 

 much that it is very prominent. Probably the condition of the tail has relation to the 

 more active pelagic habits of the larval animal at this period. 



The development of the caudal region in the salmon was observed at the fortieth day 

 after fertilisation. The tip at this stage is very transparent. The termination of the 

 notochord is gently curved upward and ends in a somewhat blunt point, a short distance 

 within the free border, the cells ceasing before the tip is reached. The notochordal 

 sheath is well marked. Above the notochord the neurochord is about the same breadth. 

 The embryonic fin-rays stretch outward as in the marine Teleosteans. Thus the embryo 

 has reached at this time a more advanced condition in regard to the notochord than the 

 larval wolf-fish in the early months. 



In the newly hatched salmon, again, the tail (PL XXVIII. fig. 1) has attained a 

 degree of development comparable with that of the wolf-fish at the stage shown in 

 PL XXVII. fig. 2, for the true fin-rays have made their appearance in addition to the 

 transient embryonic rays, though the great increase in cellulo-granular tissue obscures 

 both. On the tenth day the fin-rays number about twenty, and they abut on the 

 hypural cartilages. They are split a short distance from their origin, and blend, in 

 ordinary views, in the embryonic fibres at the tip and the cellular stroma of the organ. 



The hypural elements have also increased considerably, and show a cartilaginous 

 structure, forming a clear space behind the notochord. The notch remains in the margin 

 beyond the tip of the chorda, indicating perhaps the dorsal and ventral lobes ; but the 

 tail is narrower, and the posterior margin is less curved. 



When a fortnight old, lines of pigment occur in the tail, along the fin-rays, leaving 

 clear intermediate spaces. The arteries run along the latter, and the veins return by the 

 dark lines. There is now no notch superiorly to indicate the tip of the notochord, and 

 the free margin is somewhat undulated. The upper border of the tail is more prominent 

 than the corresponding lower margin, just as we see in Anarrhichas. The segmentation 

 of the fin-rays produces wavy lines in the tail. Already the curved portion of the noto- 

 chord is diminishing in proportion to the rest of the tail, and is now much obscured by 

 pigment. Between the fourth and fifth weeks the articulations of the cartilaginous 

 caudal rays produce three wavy vertical lines, with their convexity directed backward. 

 The rays are also more distinct, and for the greater part of their length are free from 

 pigment, the base alone possessing it. The posterior margin is uneven — from crenations, 



