ak ! 
sodium, each worked out to a point, are placed on the 
. 
369 
es 
NATURE 
205 
pads of filter paper. From each of the troughs a wire 
passes to a key so as to enable the experimenter to stop 
the current at pleasure, and from thence the current 
passes to the galvanometer. They then lay the eye ona 
glass support between the cushions, and carefully adjust 
the clay-points so that the one touches the cornea and 
the other the transverse section of the optic nerve, or the 
one may touch the surface of the nerve and the other its 
transverse section. On opening the key, a deflection of 
the galvanometer needle is at once obtained to the extent 
of about 600° of the galvanometer scale, placed at a 
distance from the mirror of the galvanometer of about 
26 inches. This deflection is a measure of the natural 
electro-motive force of the eye. The troughs are now 
covered over with an apparatus consisting of a double 
shell made of glass, and containing between the walls one 
inch of water so as to absorb all heat rays, and lastly a 
wooden box is placed over the whole, having a draw- 
shutter so as to enable the experimenter to admit light at 
pleasure. A gas flame is placed before the shutter. The 
arrangement is now complete. After observing that the 
deflection indicating the electro-motive force in the dark 
is constant, the shutter is now withdrawn so as to admit 
light. At that instant, that is, on the impact of light, a 
change is perceived in the electro-motive force. There is 
at first an increase, then a diminution, and on the re- 
moval of light there is another increase of the electro- 
motive force. Occasionally, in consequence of the dying 
of the nerve, there is only a slight increase, then a dimi- 
Nution, but the rise on the removal of light is always 
constant. The amount of change in the electro-motive 
force by the action of light is about 3 per cent. of 
the total. There has been no difficulty in demonstrating 
the effect in the eyes of the following animals, after 
removal from the body: Reftiles, Snake; Amphibia, 
Frog, Toad, Newt ; Fzshes, Gold Fish, Stickleback, Rock- 
ling; Crustacea, Crab, Swimming Crab, Spider Crab, 
Lobster, Hermit Crab. The greatest effect was observed 
in the case of the lobster, in the eye of which Messrs. 
Dewar and McKendrick found a modification in the elec- 
tro-motive force by the action of light to the extent of about 
ten percent. With the eyes of birds and mammals they 
had great difficulty. It is well known that in these ani- 
mals the great source of nervous power is an abundant 
supply of healthy blood. Without this, nervous action is 
soonarrested. This law, of course, holds good for the retina 
and optic nerve. When, therefore, they removed the eye- 
ball with nerve attached, from the orbit of a cat or rabbit 
recently killed, and placed it in connection with the clay 
points, they found a large deflection which quickly 
diminished, but all sensitiveness to light disappeared 
within one or two minutes after the eye had been re- 
moved from the animal. This fact of itself shows that 
what has been observed is a change depending on the 
vital sensibility of the parts. It was therefore necessary 
to perform the experiment on the living animal under 
chloroform. By so fixing the head that it could not move, 
and by removing the outer wall of the orbit so as to 
permit the clay points to be applied to the cornea and 
nerve, the same results have been obtained in the case 
of the cat, rabbit, pigeon, and owl. 
Without going into minute detail, which the space 
allowed for this short article will not admit of, the results 
_of this inquiry have been as follows :— 
1. That the specific effect of light on the eye is to 
change the electro-motive force of the retina and optic 
nerve. 
2. That this last applies to both the simple and to the 
compound eye. 
3. That the change is not at all proportional to the 
amount of light in lights of different intensities, but to 
the logarithm of the quotient, thus agreeing with the 
_~ psycho-physical law of Fechner. 
4. That those rays, such as the yellow, which appear to 
our consciousness to be the most luminous, affect the 
electro-motive force most, and that those, such as the 
violet, which are least luminous, affect it least. 
5. That this change is essentially dependent on the 
retina, because if this structure is removed, while the 
other ,structure of the eye lives, though there is still an 
electro-motive force, there is no sensitiveness to light. 
; That this change may be followed into the optic 
obes. 
7. That theso-called psycho-physical law of Fechnerdoes 
not depend on consciousness or perception in the brain, 
but is really dependent on the anatomical structure and 
physiological properties of the terminal organ itself, inas- 
much as the same results as to the effect of light are 
obtained by the action of the retina and nerve without 
the presence of brain. 
The method of investigation pursued by Messrs. 
McKendrick and Dewar is applicable to the other 
senses, and opens up a new field of physiological research. 
The specific action of sound, of the contact of substances 
with the terminal organs of taste, and of smell, may all 
be examined in the same manner ; and we are in hopes 
of soon seeing results from such investigations. 
ON THE FERTILISATION OF FLOWERS BY 
INSECTS AND ON THE RECIPROCAL 
ADAPTATIONS OF BOTH 
Il. 
In what manner the hive- and humble-bees obtain the 
honey of the flowers 
[x the last number the use the bee makes of its complex 
sucking machinery, when emptying the deepest 
honey-tubes or spurs accessible to it, was stated in de- 
tail; we have now to show the different movements and 
positions the separate parts of the mouth undergo, when 
the bee is obtaining honey less deeply placed, or when it 
is about to collect the pollen of flowers, or when it folds 
together the whole sucking apparatus into the cavity of 
the head in order to employ its jaws or to rest. 
(2) In order to obtain the honey out of tubes or spurs of 
less depth the bee need not turn the cardines forward; 
these remain at rest in their backward position, the 
tongue remains consequently embraced by the maxilla 
and labial palpi, and only the base of the tongue is alter- 
nately protruded and withdrawn, by which motion the 
terminal whorls of hairs are alternately immersed into 
the honey and withdrawn into the sucking-pipe. 
(3) While the bee, in order to suck honey, flies 
from flower to flower, it carries its sucking apparatus 
stretched forward so as to be able to put it directly into 
the opening of the honey-tube, but its tongue is perfectly 
enclosed between the labial palpi and the maxillz ; the 
delicate whorls of hairs are protected by that from any 
injury they might receive, when introduced into the 
flowers, and the terminal joints of the labial palpi are not 
prevented from serving as feelers. Consequently during 
the flying from flower to flower the base of the tongue is 
folded into the extremity of the tubular mentum, the 
cardines are turned backwards, whilst the lora can be 
directed downwards (Fig. 4), forwards (Fig. 2) or back- 
wards, in proportion as the bee is about to obtain the 
honey from shorter or longer tubes. 
(4) The parts of the mouth must be held in the very 
same position when the bee wishes to pierce tender cellular 
textures by means of the tips of its maxilla. It executes 
this sort of process, sometimes in order to obtain the fluids 
of juicy flowers which do not secrete nectar, as for 
instance Hyacinthus orientalis, Orchis mascula, morio 
and /atifolia, sometimes in order to break open honey- 
tubes which are too deep to be emptied by the bee in the 
