THE ADIPOSE LOBE OP THE PELVIC PIN OP THE SALMON. 727 
Some specimens of Mugil cephalus whicii had lain many 
years in spirit were the next that came to hand. In these a 
triangular patch of skin devoid of scales was found in the 
normal position of the accessory scale ; there was no trace of 
a lobe. 
A few genera of Acantbopterygian fishes in which tlie 
accessory scale has been figured were lastly examined. In 
these there was a small flap or thread of skin in the normal 
position, but the skin was entirely devoid of stiffening matter 
of auy sort. Among the MullidEe, Mullus barbatus and 
M. furmutetus showed such a condition; in the former, 
howevei', ’the thread of skin was very slendei', and the latter 
was badly preserved, so that it was not possible to judge of its 
normal condition. Among the Spai’idae, Sargus unimacu- 
latus shows a distinct flap of skin, but the occurrence 
of any projecting tissue is very doubtful in another species 
of Sargus (not identified), and the same must be said of 
Charax puntazzo. At all events there is in these forms 
a certain area at the outer angle of the ventral fin which is 
covered by skin, but is devoid of scales. 
V. Homology and Function. 
In the foregoing pages we have examined the structure 
and the development of the adipose lobe of the pelvic fin of 
the salmon, and have seen from both these points of view that 
it resembles a body-scale. We have further noted that the 
presence of an accessory scale, or, in some instances, of a flap 
of skin in a corresponding topographical position, is a wide- 
spread feature of Teleosteau fishes. That the adipose lobe is 
morphologically neither more nor less thai^ a large body-scale 
which has never broken through its surrounding pocket is 
too obvious to require proof, but it would not be right to leave 
such a remarkable 'structure with no more than a platitude of 
this kind. The possibility of deriving the dermal fin-rays 
from body-scales, through the intermediary of a fin-like scale, 
such as we have in Sal mo, occurred to my mind before my 
VOL. 58, PART 4. — NEW SERIES. 48 
