1865.] OF PHYSALUS ANTIQUORUM. 209 
the mode of distention of the skin of the animal he dissected (P. Z.S. 
1856, p. 192, pl. xxv. f.8); but these will be found on comparison 
hardly to show the true manner in which distention js permitted. 
A similar vertical section through the skin, as deep as the muscle, 
revealed the small depth of the blubber, from 2 to at most 4 inches, 
and that between it and the true skin there was scarcely any appre- 
ciable difference, so intimately and continuously were the fibres inter- 
woven. The only difference was in the rather wider meshes inwardly, 
the interspaces there containing oil, although in very limited quan- 
tity. 
The pectoral fins were flattened, narrow-pointed, and curved; in 
appearance they were not unlike the figures given by Eschricht* of 
the fin of Péerobalena minor (Balenoptera rostrata, F ab.). 
In position, and while attached to the body, one measured along 
the border of the anterior curve 75 inches, and in the posterior mar- 
ginal curve 57 inches. When cut off, the measurement from the 
articulation of the shoulder-joint to the terminal point in a direct 
line was 85 inches. 
The dorsal fin was falciform, laterally compressed, and erect ; its 
height 15 inches, and its antero-posterior length at the base 13 inches. 
The tail in extent across to the extremity of either fluke was 133 
inches, and its breadth at the root 37 inches. 
I am not aware that the exact manner in which the tail acts in 
this tribe of animals is perfectly agreed upon among writers; for 
although John Hunter? expresses himself to the effect that the mo- 
tion of the tail is similar to that of an oar in sculling a boat, and 
again, that from its horizontal position the animal is impelled up and 
down in the water, thus giving the necessary opportunity of breath- 
ing, yet Dr. Knoxt admits the difficulty in understanding the mode 
of progression, and further states that this takes place by a series of 
bounds, caused by the spring of fhe incurved tail, the immense 
strength of the flexors and extensors giving it such a counter force 
against the water as to impel the animal along and upwards accord- 
ing to circumstances. 
That each of these mechanical applications of the tail to certain 
motions does take place is more than likely, although at first it does 
not seem so very clear how the mere flapping of a horizontal tail 
produces a steady onward gliding movement, which no doubt occurs 
without the necessity of continually rising and falling in the water. 
The Sperm Whale, according to Beale§, “ when undisturbed, passes 
tranquilly along just below the surface of the water, at the rate of 
about three or four miles an hour, which progress he effects by a 
gentle oblique motion from side to side of the ‘flukes,’ precisely in 
* Untersuchungen iiber die Nordischen Wallthiere, 1849, tab. 8. figs. 1, 2. 
t ‘ Observations on the Structure and Economy of Whales,’ Palmer’s edition 
of his works, 1837, vol. iv. p. 331. 
{ ‘Cat. Prep. of Whales,’ No. 4. Iam indebted to the kindness of Dr. Gray 
for a perusal of this scarce pamphlet, which contains much information on the 
anatomy of Cetacea. : 
§ ‘ Nat. Hist. of the Sperm Whale,’ p. 39. 
Proc. Zoox. Soc.—1865, No. XIV. 
