LIGHT-PRODUCING ORGANISMS 11 



tories with the possible exception of Pholas, Phyllirrhoe 

 and squid. Although earthworms and myriapods which 

 produce light are found in the United States, they are 

 rather rare and seldom observed forms. 



Not only adult forms but the embryos and even the 

 eggs of some animals are luminous. The &gg of Lampyris 

 emits light within the ovary and freshly laid eggs are 

 quite luminous. The light does not come from luminous 

 material of the luminous organ adhering to the egg when 

 it is laid but from within the Qgg itself. Pyrophorus eggs 

 are also luminous. The segmentation stages of Cteno- 

 phores are luminous on stimulation, as noted by Alhnan 

 (1862), Agassiz (1874) and Peters (1905), but the eggs 

 themselves do not luminesce. Schisopod larvm (Trojan, 

 1907), Copepod nauplii (Giesbrecht, 1895), Chcetopterus 

 larvce (Enders, 1909), and brittle star plutei (Mangold, 

 1907) also produce light. 



Apparently there is no rhyme or reason in the distribu- 

 tion of luminescence throughout the plant or animal king- 

 dom. It is as if the various groups had been written on 

 a blackboard and a handful of sand cast over the names. 

 Where each grain of sand strikes, a luminous species 

 appears. The Ccelenterates have received most sand. 

 Luminescence is more widespread in this phylum and 

 more characteristic of the group as a whole than any 

 other. Among the arthropods luminous forms crop up 

 here and there in widely unrelated groups. In the mol- 

 lusks, excluding the cephalopods, only two luminous spe- 

 cies are known. Several phyla contain no luminous forms 

 whatever. It is an extraordinary fact that one species in 

 a genus may be luminous and another closely allied species 

 contain no trace of luminosity. There seems to have been 



