by Frank EF. Beddard. 13i 
likeness to the adult in this particular is soon formed in the course of 
development. But there are differences in different genera of which 
I shall not attempt an exhaustive analysis. I may point out, however, 
that in the Dolphin Lagenorhynchus acutus, Guldberg & Nansen figure* 
feetus of 110 mm. and 170 mm., in which, respectively, the head was 
either bent or in the same straight line with the body. Thus in 
comparing the sizes of this dolphin and Physeter macrocephalus, it 
becomes clear that the adult form is attained at a considerably earlier 
age in the Sperm Whale. Salenoptera borealis is another example 
which agrees with the Dolphin referred to, and not with the Sperm 
Whale. For a fetus of this whale, which reaches in the adult 
condition a length of 50 feet or exceptionally} even rather more, the 
foetus has the head bent down at a length of 15 inches. It does not 
therefore acquire the adult condition in this respect until a later date 
than is seen to be the case in Physeter macrocephalus. On the other 
hand, the remarkable series of MJegaptera embryos described by 
Kikenthal seem to show that this Cetacean rather resembles 
Physeter than its nearer allies. So, at any rate, I judge from the 
figures and measurements of two fetus at, or near, the critical age 
which demonstrate the change under discussion. For in an embryo? 
of about 34 inches in length the head was set at quite a right angle 
to the long axis of the body, while in one of about twice that length 
the head was very nearly in the same straight line with the body. 
More detailed comparisons are unnecessary to accentuate this general 
similarity between the two remotely allied genera in the particular 
under discussion, which is therefore clearly of but little systematic 
importance. 
A second important feature in which the two new feetus may be 
compared with the older feetus concerns the proportion of the head to 
the trunk. ‘The actual measurements which I made of the two fetus 
are as follows : 
Smaller foetus, total length 114 mm. (= 44 inches about) ; head 
32 mm. 
Larger feetus, total length 241 mm.; length of head 65 mm. 
* On the Development and Structure of the Whale. Pt.1. On the Develop- 
ment of the Dolphin, Bergen’s Mus., 1894, Taf. III. figs. 1 and 2. 
+ Monographs of the Pacific Cetacea. II, The Sei Whale (Balxnoptera 
borealis, Lesson). 1, History, Habits, ete., by R. C. Andrews, and 2, Anatomy 
of a Fetus of Balenoptera borealis by H. von W. Schulte. 
t Loe, cit., Taf. 2, fig. 20, showing a young embryo with head bent on body 
and fig. 21, an older embryo in which the head has nearly—if not quite— 
straightened out. 
