444 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCTETY. 
described, passes over the surface of the septal membrane, 
perforates it, and its fibres unite with the distal cells. 
As to the function of the eyes in Pecten, Patten, 
apparently in order to surmount the difficulty of an 
animal having more than two eyes of such complexity, 
has advanced the theory that they are organs for the 
reception of solar energy, which is then transmitted along 
the optic nerves to centres where it is used in the 
building up of protoplasmic compounds, or in metabolism 
generally. Leaving aside the physiological objections to 
such an idea, which has been severely criticised by more 
recent workers, it will be seen that Patten assumes the 
structures are such as would be evolved for the purpose of 
receiving solar energy, the rays of which are concentrated 
by the lens. 
A lens, however, cannot increase the solar energy 
falling upon its surface, it can only cause the rays to fall 
upon a smaller area of the retina. Ina review of Patten’s 
paper in the Q. J. M.S. for 1887, it was pointed out that 
“a naked epidermic surface of area equal to that of the 
lens would present a perfect instrument for the absorption 
of solar energy.” 
Observations carried out on Pectens living in the 
tanks at the Port Erin Biological Station have shown that 
they are very sensitive both to ight and to sound waves. 
If a dark object 1s moved in front of a Pecten so that the 
shadow falls over the eyes, a rapid closing of the valves 
immediately follows. A sudden increase in the illumina- 
tion apparently produces no effect. The flashing of the 
light from a bright lantern on the animals, which have 
the valves open and the tentacles extended in the darkness 
of the aquarium at night, causes no retraction or closure 
of the valves. 
It is obyious that with a lens forming an image on a 
