DEVELOPMENT OF LIGHT-OEGAXS 257 



The fat cells, when they first leave the fat-spheres, are large 

 and nearly circular, though somewhat irregular in outline. Their 

 nuclei are large and fairly distinct, though they are often more 

 or less concealed by the fat-globules which are colored dark 

 by osmic acid. Their nuclei are not elongated and distorted, 

 as Williams described. The cytoplasm of the cells show a 

 more or less vacuolated condition. Soon after the fat-cells 

 are liberated from the fat-spheres and become distributed along 

 the hj^Dodermis, their cells divide rapidly, and it is not uncommon, 

 in sections of this stage, to find them in mitosis. Occasionally 

 the fat-cells can be observed dividing before' leaving the fat- 

 spheres, but in all such cases, the spheres have ruptured and 

 are lying against the basement membrane. 



It is true that there are numerous leucocytes present about 

 the fat-spheres and the newly liberated fat-cells, though the 

 enveloping membrane of the fat-spheres described by Williams 

 does not appear to be present. The large leucocytes are espe- 

 cially abundant, and it is possible that they function in break- 

 ing do\\Ti the fat-bodies. The small leucocytes are also present 

 in considerable numbers, and it seems possible that they may also 

 have a similar function. Some of these leucocytes are un- 

 doubtedly functioning in breaking up some of the fat-masses 

 for the actively developing tissues. Neither the small nor 

 the large leucocytes are observed among the cells of the 

 light-organ, though they are often found lying near, or in the 

 region of, these cells. 



The hypodermis at this stage also shows evidence of considera- 

 ble activity, for its cells are much elongated (fig. 12) and some 

 show evidence of division. Sections of some of the larvae at 

 this stage do not show these elongated hj^oodermal cells, though 

 as a rule they appear to be attenuated to a considerable extent. 

 It seems possible that the stage of their elongation may not 

 correspond with the early origin of the light-organs, so the two 

 structures ma}^ not appear the same at the same stage in different 

 specimens. 



Branches from the larger neighboring tracheae make their 

 appearance very early, and at this stage these smaller tracheae 



