182 F. X. WILLIAMS 



tory they hatch in less than three weeks. They are faintly 

 luminous. 



4. The larva of Photinus is subcylindrical and slender, that 

 of Photuris broad and flattened-fusiform. Both are carnivorous 

 and nocturnal. They feed also after the second hibernation and 

 transform into pupae in May or June. 



5. The pupae retain the two larval lights on the eighth abdomi- 

 nal segment, and in addition, the pupa of Photuris has a diffuse 

 glow, especially in the head and thorax. The pupal period prob- 

 ably does not exceed twenty days. 



6. Both sexes of Photuris are active flyers and runners. The 

 female has a voracious appetite. Only the male of Photinus is 

 an active flyer. 



7. The photogenic organs of all Lampyridae thus far studied 

 are formed on the same general plan. Each organ consists of 

 an upper or reflector layer, and a lower or photogenic layer of 

 cells. Tracheae and nerves penetrate both layers but are more 

 highly developed in the lower. The cuticle which overlies the 

 photogenic organs is usually translaucent. 



8. There are in general two views on the derivation of the 

 photogenic organs in Lampyridae, the one holds that they are 

 derived from the hypodermis, and the other that they come 

 from the fat-body. The latter view is the correct one, as Vogel 

 ('13), and I have shown. 



9. The development of the adult photogenic organ was studied 

 in Photinus consanguineus. Here it is first seen in larvae near 

 pupation. It is derived directly from the fat-body by the expul- 

 sion of its cells, which migrate to the ventral hypodermis. This 

 cell-expulsion is effected or aided by the inflection of an invest- 

 ment which partly envelopes the fat-spheres here as also espe- 

 cially in the thoracic region. Numerous haemocytes apply them- 

 selves to these investments. No cell division was noticed during 

 this process. 



10. The cells thus liberated from the fat-spheres to form the 

 photogenic organ, accumulate as an indefinite mass on the hypo- 

 dermis and there proliferate. Two layers are gradually formed. 

 During this process, the large albuminous granules common to 



