DEPARTMENT OF MARINE BIOLOGY. 157 



Although the luciferins and luciferases of different luminous animals are 

 certainly similar substances, they are not identical. Through the kindness of 

 Professor Dubois I have obtained some luminous organs of Pholas dadylus 

 preserved in sugar. Pholas luciferin will give no light with Cypridina luci- 

 f erase and Cypridina luciferin will give no light with Pholas lucif erase. No 

 doubt these two forms are too distantly related for the interaction of the 

 luminous substances. The specificity of different luciferins. especially in rela- 

 tion to the color of the Ught produced, offers a most interesting and important 

 field for subsequent research, and I hope to be able to present more data on 

 this subject in the near future. 



A Study of Luminous Insects, by Ulric Dahlgren. 



The writer spent the months of March and April 1918 in the South, study- 

 ing and collecting luminous organisms. Starting from New York on a Mal- 

 lory steamer for Galveston, very Httle of va^ue was seen at sea. Varying 

 numbers of luminous plankton appeared and part of each night was spent 

 in observing and attempting to identify them. The green glow of cteno- 

 phores was easily distinguished from the silvery light of Nodiluca and other 

 dinoflagellates. One interesting observation was made at lO'^SO'" p. ni. in 

 the waters of the Gulf of Mexico. Standing at the rail, the slap of a porpoise's 

 tail was heard as he discovered the steamer and decided to move in by the 

 bow from a distance of about 200 yards off the beam pretty well aft. Look- 

 ing quickly toward the sound, the animal was seen (the night was dark) as 

 a moving luminous body w-ith a diminishing trail of several yards. Moving 

 at a speed of between 15 and 20 knots, he passed in a long, slightly curved path 

 to a position just under the bow, where he played for about 5 minutes and 

 then suddenly disappeared. The whole episode so resembled the approach 

 of a torpedo that several people who saw it drew back from the rail and two 

 women screamed, although several called out "porpoise." 



Landing at Galveston and proceeding to Houston, it was found that a very 

 dry season had prevented the appearance of nearly all insects; also that it 

 was too early for fireflies. A number of trips with local collectors, by both 

 day and night, failed to show any luminous forms except some collembolids. 

 The same was true of a trip south nearly to Brownsville, where some coUem- 

 boUds and a few larvae of the common firefly, Photuris pennsylvanica, were all 

 that was found. 



Better results were obtained at Beaumont, Texas, where a few of some com- 

 mon forms were on the wing and luminous collembolids were also found ; also 

 some luminous earthworms. The finding of luminous earthworms and col- 

 lembolids here and at other localities and the continual observation of them 

 while demonstrating their light were important, because up to the time of this 

 trip their organic light production was an open question with some zoologists. 

 Such reports as had been made of the phenomenon were published in obscure 

 journals or were contradictory. The writer has followed up verbal or pub- 

 lished reports by Atkinson, Barber, and McDermott very carefully and has 

 repeatedly proven that both the collemboKds (some species) and earthworms 

 (Microscolex) do flash or glow with an autogenous organic fight in response to 

 well-known stimuhi that are used to prove the presence of such fight in other 

 well-known luminous forms. 



Several swamps and locafities were then visited between Beaumont and 

 New Orleans and a week was spent in the swamps and inland waterways 

 south of New Orleans. In all of these regions the fireflies were beginning to 

 appear and the mating habits were studied, especially the uses of the light as 



