DEVELOPMENT OF LIGHT-ORGANS 259 



pretation at this stage, the basement membrane has largely- 

 broken do^\^l, so that no very definite fine of separation between 

 the two groups of cells could be found. Since modifications of 

 a similar character were observed in the hypodermis remote from 

 the light-organ, it was concluded that these peculiarities are 

 associated with the normal metamorphosis of this tissue. 



The dark colored globules which were present in the fat- 

 cells are still present, in a small number in all the undifferentiated 

 cells of the fight-organ, but none are present in the cells that 

 are definitely known to be hypodermal. The presence of these 

 fat-globules in the fat-cefis and the cells of the developing fight- 

 organ, but not in the hypodermal cells, leads one to conclude that 

 these undifferentiated fight-organ cells are derived entirely from 

 fat-cells. 



The tracheae by this time have penetrated the light-organ 

 cells at frequent intervals, and at many places they have ex- 

 tended their cells to the hypodermis. Frequent mitotic divisions 

 are still observed among these cells. Some of the tracheal 

 cells, which appear to be grouped in masses, are frequently 

 observed lying just dorsad of the light-organ cells. As a rule, 

 several of the cells from these larger masses, extend down be- 

 tween the cells of the light-organ. These tracheae, while in an 

 immature stage of development, grow down among the light- 

 organ cells at more or less regular intervals and they resemble 

 in location those of the mature light-organs. 



A slightly later stage than figure 13, which was taken of a pupa 

 one day after pupation, is represented by figure 14. Even at 

 this stage the cells of the light-organ show no evidence of a 

 separation into the two layers, but, on the other hand, they all 

 appear to have the same general characteristics and resemble 

 very closely those of the undifferentiated light-organ cells shown 

 in figure 13. It seems evident, however, that their cytoplasm 

 is slightly more granular and the fat-globules are sfightly less 

 abundant, but, aside from the fact that they are now four or 

 five cells in depth, there is little real difference. Emphasis here 

 should be placed upon the fact that afi the undifferentiated cells 

 of the fight-organ ([/), at this stage, appear to be alike histologi- 



