THE ADIPOSE LOBE OP THE PELVIC PIN OP THE SALMON. 729 
this homology is true, it should be noted at the same time 
that the ventral ramus of the head is wanting, as is also all 
trace of a ventral half ; moreover, while the lepidotrichia are 
characteristically jointed, the splint is composed of a single 
piece. ^ These points are apparent in Text-fig. 3. It was 
further observed that the splint lies in a pocket of connective 
tissue, which in section resembles a scale pocket (see fig. 4, 
Sp. h.). The resemblauce does not necessarily prove the 
homology of the two structui’es ; it is merely satisfactory as 
not dispelling the idea. Taking’ the sum of these considera- 
tions we must suppose that we have to deal with the head 
Text-pig. 3. 
The first (outermost) lepidotrich of the pelvic fin, together with 
the splint of hone which supports the adipose lobe, seen from 
the inner aspect. Sp. Bony splint (probably = dorsal half of 
a tenth lepidotrich). H. d. Head of dorsal half of first lepidotrich, 
with its dorsal ramus d., and ventral ramus v. H. v. Head of 
ventral half of 1st lepidotrich. 
and dorsal ramus of an additional lepidotrich which exhibits 
certain scale-like properties. ^Vhether this lepidotrich is in 
the process of development or whether it is the vestige of a 
once fully developed ray I cannot at present decide with 
certainty, but its secondary fusion tends to show that it is 
vestigial. The exact homology of the adipose lobe itself is 
more obscure; that it arises as a scale we have seen. It is 
unlikely that it ever functioned as a fin-ray, or part of a fin- 
’ This is not necessarily a dissimilarity, for it will be noticed that the 
heads of the lepidotrichia are also devoid of joints, and the splint is 
only equal in size to the head of a fully developed Lepidotrich. The 
unjointed condition of the heads of the Lepidotrichia is, without doubt, 
due to secondary fusion. 
