DEVELOPMENT OF LIGHT-ORGANS 263 



tion of the light-organ is very rapid as soon as luminescence 

 ceases and that the leucocytes are probably the chief agents in 

 destroying it. 



SUMMARY 



1. The first indication of the formation of the light-organs, 

 in the embryo, is noticeable at the age of fifteen days, just as the 

 embryo revolves from its backward-turned position and starts 

 to coil up. 



2. At this time groups of fat-cells, with their large globules 

 which are colored dark by osmic acid, migrate ventrally in 

 segment eight and come to lie in the region of the future light- 

 organs. These undifferentiated light-organ cells are now con- 

 tinuous with the groups of fat-cells dorsal to them. 



3. As soon as the fat-cells become localized in the region of the 

 future light-organs, their dark colored globules become smaller 

 in size and fewer in number. In fact, in the fifteen-day embryos 

 there appears to be a gradual gradation from the cells lying next 

 to the hypodermis, Avhich contain smaller and fewer of these 

 globules, to the fat-cells near the central part of the body, which 

 contain more and larger globules. 



4. In the sixteen- and seventeen-day embryos the light-organs 

 are regular in outline, and they have become separated from the 

 other fat-cells. The fat-globules are now smaller and fewer in 

 number than on the fifteenth day. All cells that compose the 

 light-organ are apparently now of the same histological structure. 



5. At the age of twenty days there begins to take place a 

 differentiation of the cells of the light-organs into the photogenic 

 and reflector areas. 



6. At the age of twenty-two days the light-organs become 

 functional and appear as two minute spots of light. 



7. The larvae emerge on about the twenty-sixth day of incu- 

 bation. 



8. These larvae require nearly two years (about twenty-two 

 months) to reach maturity, at which time they pupate. 



9. In mature larvae, about one-half day before pupation, 

 the cells of the fat-spheres, which lie near the hypodermis in 



JOURNAL OP MORPHOLOGY, VOL 36, NO. 2 



