SEA-FISILERIES LABORATORY. 423 
the surface of the body, and somewhat between the 
ganglia. 
They can be seen in dissections as two minute delicate 
white bodies, if the connective tissue above the cerebral 
and pedal ganglia is carefully removed, and are perfectly 
spherical in shape, with a diameter of 0°17 mm. 
The position of the otocysts outside the foot is 
interesting, as the pedal ganglia are also completely 
outside the foot in Pecten. There can, however, be no 
question here of the nerve innervation, for the nerves can 
be traced directly out from the cerebral ganglia without 
any connection with the cerebro-pedal connectives, thus 
rendering further proof to the theory that the otocysts 
are always innervated by the cerebral ganglia, even when 
they are connected with the cerebro-pedal connective and 
he in close proximity to the pedal gangha. The nerves 
enter the otocysts on the sides facing the cerebral ganglia, 
and are thus quite short. The otocysts in both P. 
opercularts and P. maaimus are spherical closed sacs, the 
internal cavity of which is bounded by a layer of sense 
cells. In this cavity there is situated an otolith. This 
appears in P?. opercularis as a large ball, formed of small 
erystals of irregular shape, as if a heap of fine detritus 
had been heaped together. The otolith thus formed fills 
almost completely the cavity of the otocyst. In 
P. maaimus, I have only found some larger and more 
scattered crystals (otoconia) in the otocyst. In the adults 
of both species examined, the otocyst has no duct 
connecting the cavity with the external world. 
Tur Ospurapia.—These paired sensory structures, 
named by their discoverer, Spengel (38), organs of smell, 
and which are of general occurrence in Mollusca, are not 
highly developed in Pecten. They cannot be detected 
without the aid of microscopic sections, and though 
