52 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



Luminescence. — One of the most strilvinglv familiar sights of the sea beach 

 at night during the wami months of the year is the display of phosphorescence 

 in the lireakers. ]\Iany of the small plankton forms are capable of producing 

 this light, such as crustaceans, worms, and coelenterates, as ^Yell as some of the 

 bacteria. No inconsiderable part of it, however, is due to these minute dino- 

 flagellates. It is probable that the bacteria play little if any ])art in the ordi- 

 nary exliibitions of phosphorescence of the sea, since the light they produce is 

 a continuous one and not a sudden flash, such as may be observed in the breakers 

 01' in the water elsewhere when it has been disturbed. 



N^odiluca was the first one of the group which received recognition as a 

 light-producing organism, observations having been made on it as far back as 

 1717 (Dahlgren, 1915-16). Since that time casual notes and detailed studies 

 on this form have been numerous, as a result of its wide distribution, great 

 al)undance and relatively large size, combined with the brightness of the light 

 which it produces. It is probable that other forms somewhat similar in struc- 

 ture to Noctiluca, as Leptodiscus and Craspedotella, are also huninescent, but 

 thus far no CA^idence has been brought forth to bear out this conclusion. 



It was not until some time after these first observations made on Xodiluca 

 that the light-producing qualities of the remainder of the dinoflagellates were 

 noted. This was due to the work of Michaelis in 1830. He figured at least 

 nine species of Pendinimn, Ceratium, and Prorocentrum, with a descrijitiou 

 of tlie light produced by them. These observations were confirmed by later 

 investigators, but without the exactness of detail that has been given for 

 Noctiluca. 



Among the Peridiniidae and G\Tiinodiniidae very many, if not most, of the 

 genera contain light-bearing species. Observations on these groups have been 

 almost wholly confined to the thecate forms, due to their greater al)undauce 

 and the comparative ease with which they may be studied. Those that have 

 received the most attention are Ceratium tripos, Gonyaulax polyliedra, Peri- 

 dinium hahamense, and a colonial species of Pcridinium observed by Dahlgren 

 (1935-16) in the waters of the Delaware and Chesapeake bays. 



Experiments made by us at the Biological Station at La Jolla, California, 

 have also been mainly on the thecate forms. The method of study has been 

 the isolation of individuals in a watch glass with a small amount of filtered 

 water, which has been examined both before and after the experiment to make 

 certain that no other organisms were present. These isolated individuals were 

 then tested by various stimuli, jarring the watch glass or adding fresh water, 

 alcohol, ether, or other chemicals in A-ery dilute quantities. It was found in 

 this manner that nearl}^ all the species of Peridinium, Ceratium, and Gonyaulax, 

 then common in the plankton hauls, were capable of producing light. Light 

 was never observed in a watch glass containing a single organism without the 

 application of stimuli, though it was abundantly exhibited in the glass dish 

 near by containing the usual plankton haul. This would indicate the necessity 



