Fig. Z7. The successive phases m the appearance of the photogenic units in the photophore on the -rp- "[J^J 



left fif^h thoracc Hmb of Systellasp.s affims. The figures are taken .n order from the appearance ot the structures 



seen in passing in the direction indicated by the arrow in Fig. 26. 



a. Large nucleus, precursor of photogenic unit. 



b Nucleus with chromatin becoming less dense and forming a more uniform reticulum. 



; Nucleus degenerating, vacuoles appearing within the limiting membrane, and the first deposits of granular 



substance occurring on the inner side of the limitmg membrane. 

 d Nucleus almost disappeared, vacuoles still present, and granular deposits larger and more numerous. 

 e Only the granular deposits now remain, regularly arranged and extending centripetally. ^. , ^ „ 



f. Enlargement of the regularly arranged granular masses almost obliterating the central cavity, which finally 



disappears completely. 



grJ. granular deposit; Un. limiting membrane; vac. vacuole; d.n. degenerating nucleus. 



