340 RUPEUT VALLENT1N AND J. T. CUNNINGHAM. 



the cells of which the ridges consist. Light emanates exclu- 

 sively from these ridges, and in the natural state of the Pen- 

 natula appears only in consequeuce of a stimulation ; a single 

 touch at any point of the colony may cause a luminous current, 

 so to speak, to run through the whole. But the luminous 

 matter can be caused to give out light after separation from 

 the Pennatula by rubbing or by the application of fresh 

 water. 



In Pyrosoma there are two small luminous organs in each 

 zooid near the external end of the branchial chamber. Each 

 is composed of spherical cells and is attached to the inner 

 surface of the outer layer of the integument. The eells contain 

 a substance soluble in ether. 



Pholas possesses several patches of excreting epithelium on 

 the internal surface of the mantle ; the cells of these patches 

 give off a mucus which is in great part composed of fat and is 

 luminous. 



In Phyllirrhoe the cells which emit light are not superficial 

 but are the ganglionic cells of the peripheral nervous system; 

 but the light is due, not to the nervous matter properly speak- 

 ing, but rather to a substance associated with the nervous 

 matter, a substance which is soluble in alcohol and ether, and 

 which gives out light when agitated even after the death of the 

 animal. 



It is evident then that there is no very clear connection 

 between our observations and the views of Panceri. If, as the 

 latter seems to think, the property of luminosity is always 

 confined to a substance of a fatty nature, we connot say in 

 which part of the photospheria of Nyctiphanes the fatty 

 substance occurs ; we can only repeat that we saw light emitted 

 only from the surface of the reflector. 



