PLATE 2 



EXPLANATION OF FIGURES 



6 Sagittal section of the light-organ of a fifteen-day embryo, which shows the 

 light-organ in a very early stage of development. F, fat-cells; FG, fat-globules; 

 H, hypodermis; T, trachea; U , undifferentiated cells of the light-organ. 



7 Sagittal section of the light-organ of a seventeen-day embryo. C, cuticula, 

 F, fat-cell; H, hypodermis; M, muscle; T, trachea; U, undifferentiated cells of the 

 light-organ. 



8 Sagittal section of the light-organ of a twenty-daj^ embryo, which shows a 

 beginning of the differentiation of the cells into the two layers of the mature light- 

 organ. C, cuticula; F, fat-cell; H, hypodermis; P, photogenic layer; R, reflector 

 layer. 



Note. All the material that was used for the histological preparations that are 

 illustrated on this plate and the three following plates was fixed in Fleming's 

 fluid and stained in Heidenhain's iron hematoxylin. 



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