THE ADIPOSE LOBE OF THE PELVIC FIN OF THE SALMON. 721 
The aggregation of connective tissue in which the accessory 
scale is embedded does not at this period reach the splint of 
bone which in the adult forms the support of the adipose 
lobe, which seems to indicate that the final condition is 
secondary. Not until No. 10 does the papilla lose connection 
with the bod 3 ^-wall on its inner aspect and become a free 
lobe. 
In No. 11 the adipose lobe, though still relatively small, in 
outward appearance resembles the adult condition, only its 
outline is curved rather than angular. Vei’tical longitudinal 
sections of this specimen were prepared, and such a section 
containing the adipose lobe is depicted in fig. 8. The adipose 
lobe [Ad.) is seen lying in the angle between the body-wall 
and the ventral (pelvic) fin [V. F.). The epidermis (Np.) has 
been very considerably damaged, but a trace of it still 
remains. A number of body-scales {Sc.) are seen, cut in 
various planes; they have not yet broken through their 
scale-pockets {Sc. p.) The accessory scale {Sc. A.) is cut 
somewhat obliquely, and is seen deeply embedded in the 
tissue of the adipose lobe ; at this period it is scarcely 
distinguishable structurally from the normal body-scales, for 
ii- displays the characteristic thickened ridges, though in a 
much less marked degree. It is considerably longer than 
an)’ of the normal body-scales ; this does not appear in the 
drawing, but can easily be observed by following its course 
through the serial sections. Its proximal extremity, too, is 
much more deeply seated than that of the normal scales. 
(2) Summary of the Development and Mode 
of Growth. 
In the course of development the formation of the bon)’ 
splint, which connects the first fin-ray with the base of the 
adipose lobe occurs at the same titne as that of the fin-rays 
— i.e. long before there is any trace of the body-scales. 
It is plainly visible in sections from Specimen 1 onwards. 
Tlie body-scales do not appear till Specimen G is examined. 
Only in Specimen 8 — that is to say, sixteen weeks after 
