PRESIDENTIAL ADDRESS. 537 
this essential part constitutes the whole organ ; but generally other structures are 
superadded, such as a pigment coat, reflector (‘tapetum’ of Chun), lens, and 
diaphragm, as has been mentioned in the complex organs just described. 
Numerous interesting questions at once suggest themselves in regard to these 
structures, and it is very disappointing to admit that in regard to almost every 
one the answer is a confession of ignorance. 
The first inquiry is, What is the origin of these organs, and from what primitive 
structures are they evolved? Here it is possible to say but little; there is no 
instance in which the development of these organs in the embryo has as yet been 
studied. A larva, believed to be that of Histiotewthis, came into my hands a 
short time ago, and full of hope I had a portion of the mantle cut into sections, 
but with no result whatever; there was nothing which I could interpret as the 
rudiment of such an organ. : 
Those organs occur in so many and such scattered families that it seems clear 
they must be polyphyletic. Furthermore, even in one and the same species the 
different organs are not all constructed on the same plan. In Abraliopsis, for 
example, the pallial organs are quite different from the ocular; but the most 
striking example of this sort of complexity is found in the remarkable Thawma- 
tolampas (5), which has altogether twenty-two organs constructed on no fewer 
than ten different principles. It seems difficult in such a case to resist the con- 
clusion that these organs have been separately evolved at different times, and 
perhaps from different origins, during the phylogenetic history of the species. 
This variety in the structure of these organs naturally suggests the query, Do 
these differently designed lamps give out different kinds of light? Here we have 
the observation of Professor Chun (4) on board the ‘ Valdivia’ to guide us, accord- 
ing to which in the living animal the middle ocular organ shines with an ultra- 
marine light, whilst the middle of the five ventral organs is sky-blue and the anal 
organs are ruby-red. It may also be observed that even in preserved specimens, 
when examined in a strong light, the different organs seem to shine with different 
colours, although there is under such conditions no actual emission of light. 
Furthermore, in some forms (e.g., Caliiteuthis) there are chromatophores in the 
superficial layers of the integument over the luminous organs, through which the 
light admitted must pass. A somewhat similar arrangement obtains in the 
curious structures in Chiroteuthis, which were regarded by Joubin (20) at the 
time of their discovery as ‘thermoscopic eyes,’ but which are, I think rightly, in 
the present state of our knowledge considered to be a special kind of luminous 
organ. In these instances the function of the superficial chromatophores may be 
to colour the light which passes through them. 
The question of the utility of these variously coloured lights to the creature 
poets them admits of an answer which is, at all events, extremely plausible. 
t was suggested in the case of deep-sea fishes by Brauer, and has been adopted 
by Chun in reference to the Cephalopoda. They serve as recognition marks by 
which the various species can identify their fellows ; just as certain colour patches 
in the plumage of birds enable them to find their mates, so in the darkness of the 
ocean abysses do these fairy lamps serve their possessors. Another and perhaps even 
more obvious utility is suggested by the general distribution of these organs. It 
has above been pointed out that they are, almost without exception, on the ventral 
aspect of the body, that is, the inferior surface in the position in which the animal 
habitually ‘swims. It must happen, therefore, that when the creature is moving 
over the floor of the ocean in the quest for food, this must be illuminated by its 
lamps, and the advantage of a series of searchlights playing over the ground will 
be at once apparent. 
Finally we have the question, How is the light produced?» To’ this we can 
only say that this is an instance of the transformation of one kind of energy into 
another. We are quite familiar with the production of heat in the animal body 
by the processes of oxidation which go on in it; we are also familiar with the 
production of kinetic energy when a muscle contracts under a ‘nervous stimulus ; 
and we are also aware that electric discharges are produced under similar condi- 
tions in certain organs of the Torpedo and other fish, The production of light is 
