PLATE 5 



EXPLANATION OF FIGURES 



15 Cross-section of the fourth stage in the development of the adult light- 

 organ, taken four days after pupation. It illustrates an early stage in the differ- 

 entiation of the light-organ into two layers. C, cuticula; H, hypodermis; P, 

 photogenic layer of light-organ; R, reflector layer of light-organ; T, trachea. 



16 Cross-section of the fifth stage in the development of the adult light-organ, 

 taken five days after pupation. This represents a stage in which the cells of the 

 two layers of the light-organ are definitely differentiated. The dark fat-globules, 

 so characteristic of fat-cells after osmic-acid fixation, are distinctly visible in all 

 the cells of the light-organ at this stage, as well as in the four previous stages. 

 For labels see figure 15. 



17 Cross-section of the adult light-organ fully developed. C, cuticula; ECN, 

 nucleus of tracheal end-cell; H, hypodermis; N, nucleus of photogenic cell; P, 

 photogenic layer; R, reflector layer; T, trachea; TC, tracheole. 



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