144 Anatomy of Sperm Whale Fetus 
to it, thus dividing it into a series of ‘‘segments.” The ridge of the 
back in this youngest feetus runs to the very end of the body between . 
the flaps of the tail. And on the ventral surface there is in the 
posterior region of the body a sharp edge which similarly runs to the 
end of the tail. In the older fcetus, the ventral ridge alone reaches 
the very end of the tail; the dorsal ridge terminates about half way 
between the two flukes. As to the latter, the youngest foetus shows 
an embryonic condition of the tail flukes, indicating its youth, which 
has been noted in other whale fetus. It is represented in the 
accompanying figure (fig. 10). In the older fcetus the flukes (fig. 11) 
TeExt-FIG. 11. 
Oxuper Ferus. 
Tail fin. A, from ventral surface. B, from dorsal. 
have not yet attained to the proportions of the adult. As was the 
case with Hentschel, I could find no asymmetry in these flaps which 
has been asserted to exist. 
ANAL FIN. 
There are two remaining features about the tail which require mention. 
I think that it will be admitted from an inspection of Plate X XITI, 
fig. 1, and a comparison of that fignre with the corresponding one of 
