722 
EDWAED W. SHANN. 
hatching — is there any trace of the differentiation of the 
accessory scale, and the adipose lobe is not visible externally 
until the nineteenth week. 
A scale, which is developed in a thickened area of connec- 
tive tissue immediately above the base of the pelvic fin, is 
seen rapidly to increase in leng’th, thenceforward gradually 
to lose its ridged markings and to become homogeneous iii 
structure. This process begins about sixteen weeks after the 
hatching’ of the fish. As this specialised scale elongates it 
pushes before it the overlying tissues. First a ridge is 
formed in a horizontal direction along the body- wall ; when 
the posterior extremity of the ridg-e reaches the space between 
the ventral fin and the body-wall, it leaves the latter and 
forms a slight pi’ojectiug papilla. The papilla is at first 
conical, but, as the scale continues to grow, its outer aspect 
tends to become flat, the dorsal and ventral borders become 
sharply angular owing to the pressure of the edges of the 
growing scale, and the tissues on the inner aspect become 
largely adipose, in consequence of which its marginal walls 
fall inwards into folds along the lines of least resistance, 
'i’hus we arrive at the triangular outline of the adipose lobe 
which has been described in the adult salmon. 
IV. Observations from other Teleostei. 
(1) From the examination of other Teleosteau fishes, and, 
where this was not practicable, from illustrations of such, it 
soon becomes evident that the occurrence of an enlarged scale 
at the outer angle of the base of the pelvic fin is a wide-spread 
feature of the order. 
(2) The scale is constant for a given species. 
(3) The scale is rarely absent from the Malacopterygian 
fishes, which are beyond doubt primitive Teleosteans, and is 
more constant in the less specialised forms in other groups. 
(4) The scale is seldom seen in connection with ventrals 
which are thoracic in position, and never, so far as I am 
aw'are, with those which have reached the jugular position. 
