720 
EDWARD W\ SHAXN. 
not }"et a trace of any of the other lepidotrichia, dorsal or 
ventral, in the region where the splint appears. This con- 
stitutes a marked difference from the condition in the adult 
fish, in which the junction of the splint with the dorsal half 
of the first lepidotrich occurs in the free portion of the 
fin outside the body-wall, and on a level with other 
lepidotrichia. 
In No. 4 the splint is decidedly larger than in the fore- 
going specimens, and it is more curved. It first appears as a 
crescentic ossification placed nearly in the position noted 
above, but slightly higher up, for it subtends the adductor 
superior muscle. Further back, in addition to the portion 
which goes to meet the first lepidotrich, the upper exti’emity 
of the splint still remains in section as a disc of ossified 
tissue. No. 5 very nearly resembles No. 4, but in it the 
ventral half of the first lepidotrich appears in several sections 
before the splint finally disappears, a condition Avhich is 
probably due to the greater extension of the fin (and conse- 
quently of the lepidotrichia) prior to sectioning, for it is not 
observed in the older and presumably more advanced 
specimens. In No. 5 is begun, and in Nos. 6 and 7 is 
continued, the blunting and obliteration of the primary 
fin-fold, which was so clearly defined in the younger 
specimens. 
The body-scales are first clearly visible in No. 6. From 
No. 7 onwards there is an aggregation of connective tissue 
which forms a triangular area immediately above the fin; the 
base of the triangle is formed by the body-wall, and its acute 
apex points towards the division between the two adductor 
muscles. In No. 8 an abnormally large body-scale is found 
embedded in this triangular area, and this eventually becomes 
the accessory scale, the skeleton of the adipose lobe. In 
No. 9 the accessoi-y scale is seen deeply embedded in the 
connective tissue of the body-wall at its basal anterior end ; 
at the distal end it has grown towards the surface, and, 
pushing the body-wall before it, has formed a slight pi’ojecting 
papilla. The scale does not extend to the tip of the papilla. 
