142 Anatomy of Sperm Whale Fetus 
fact that there are no great disproportions between the two fcetus 
The umbilicus is fairly exactly in the middle of the body. The length 
of the tail region is a little less than one-third of the total length of 
the animal. But the tail is proportionately rather shorter in the 
older foetus. The interest of this fact is that in the adult Cachalot, 
according to the measurements of Hentschel* (total length of whale 
1,740 cm., anus to tail end 512 cm.), the proportionate length of the 
tail region is still less. This is doubtless due to the great increase in 
the size of the head in passing from foetal to adult life upon which we 
have already commented. The navel of the adult is also pretty 
nearly exactly in the middle of the length of the body (measured 
along the ventral side). 
TExT-FIG. 9, 
OupeEeR Fearus. 
Side view of posterior part of body. D.F. = dorsal fin, + = notch of 
unknown significance. M.G = mammary groove. Other letters as in fig. 8. 
I think that a comparison of the two figures on Plate XXIII with 
fig. 1 on Plate VIII of my memoir upon the older fetus shows 
that the two younger—and especially the youngest—fotus may be 
said to possess a distinct “neck,” which has disappeared in the oldest 
of the three. The existence of a neck in other whale foetus has been 
remarked upon, and it occasionally persists in the adult (for example 
Mesoplodon mirum). 
* Zool, Anz. loc. cit., p. 420. 
