1890.] Physiology. 193 
seen to emerge from under fields of ice without air-holes, and they 
disappear from the surface with some regularity, It is only when the 
water is smooth that Cetaceans have been found asleep on the surface. 
E. Harting (Zodlogist, March, 1889) states that the roebuck is 
still found wild in Dorsetshire, and that there are a few near Wigton, 
in Cumberland ; otherwise, it is now almost entirely confined to Scot- 
land. Even in Dorset its presence is due to a reintroduction. A 
curious fact in the life history of the roe is that, though the rutting 
season is in August, the ovum lies dormant until December, when it 
developes at the normal rate. Occasionally a female roe has horns. 
The discovery in the Hebrides of Mus hibernicus, a species which, 
like Mus decumanus, has the tail shorter than the head and body, and 
the ears relatively small, forms the subject of the first article in the 
Zoblogist for June, 1889. It is a smaller and more elegant animal 
than M. decumanus, with finer fur, of a dark silvery gray, almost black 
tint, upon the back. The far of the sides is paler, and the under 
surface is silvery mouse- 
In the September issue oat the same periodical Mr. T. Southwell 
states his belief that M. Atdernicus is a hybrid. 
Alphonse Milne Edwarcs has recently described a peculiar marsupial 
from New Guinea, under the name Dactylopsia palpator, remarkable 
for the enormous length of the fourth digit of the hand, which 
nearly equals the elongate third digit of the Malagassy Aye-Aye. 
PHYSIOLOGY.! 
Nature of Knee-jerk.—There are two theories of the nature of the 
knee-jerk phenomenon : one regards the process as entirely peripheral, 
the muscle fibres being directly stimulated to contraction by the twitch 
of the tendon ; the other regards the action as reflex. Objections to 
both exist; to the peripheral theory, especially the fact that the reflex 
arc must be functional; to the reflex theory, the fact that the time 
necessary is very short—only about one-fourth that of other reflex 
actions. Dr. Lombard, who made an elaborate study of the phe- 
nomenon in 1887,? brings forward the results of experiments to prove 
the tenability of the reflex theory. These experiments were made on 
1 This department is edited by Dr. Frederic S, Lee, Bryn Mawr College, Bryn Mawr, 
Penna. 
2 See American Journal of Psychology, Vol. I. 
3 Journal of Physiology, Vol. X 
