172 APPENDIX. 



19. PAGE 26. While investigations so far have failed to explain the 

 physiology of the light, it has been found that in a perfect animal it is 

 emitted from eight opaque cords, each of which passes from a little 

 swelling at the base of a tentacle down each polyp into the covering of 

 the branch. The cords are canals in the sarcode of the branch, connect- 

 ing the hollow of each tentacle with the tubular cavities of the branch- 

 lets and stem. The microscope shows that the contents of the canals are 

 a fluid and cells ; the latter containing minute highly refracting globular 

 particles of a fatty substance, which resists decomposition long after the 

 death of the polyp itself. If these cords are ruptured, the luminosity of 

 the entire mass is excited, and the fatty cell contents is luminous after its 

 escape, and on foreign matter even after the death of the animal. 



Regarding the light, Duncan says, referring to Panceri's experiments, 

 "There is no sensible increase of temperature, and the tint of the 

 monochromatic light is azure or greenish, but never red. In this beauti- 

 ful instance of this remarkable vital luminousness there is evidently a 

 photogenic structure and an elaborated organic material capable of pro- 

 ducing light after removal from the animal. The sequence of illuminat- 

 ing the whole pen is slow, far less than that of the movement of nerve- 

 force. Yet the presence of the lowly organized nervous element indicates 

 that the regulating of the light may relate to it as its function." 



Perhaps the most magnificent of all the Pennatulidce is the tall Umbel- 

 Maria graenlandica (Plate XXI., Fig. 2), which consists of twelve huge 

 polyps, each with eight fringed arms, terminating in a close cluster upon 

 a stalk about four feet in height. This striking form was dredged by 

 the " Challenger" expedition in water over two miles in depth, where the 

 pressure is so great one can hardly realize it, and the temperature is just 

 above freezing. Sir Wyville Thompson says, that, when this splendid 

 animal was taken from the trawl, it emitted a light so brilliant that Capt. 

 Maclear found it an easy matter to determine the character of the light 

 by the spectroscope. It gave a very restrictedly continuous spectrum, 

 sharply included between the lines b and d. 



20. PAGE 27. Pavonia quadrangular is. 



21. PAGE 27. Asteronyx loveni. 



22. PAGE 27. Ophiacantha. 



23. PAGE 28. Renilla reniformis. 



