DEVELOPMENT OF LIGHT-OEGANS 247 



case of the larvae and pupae, the posterior four segments were 

 removed by scissors and placed in the fixers. 



The material was all imbedded in paraffin. In the case of 

 the embryos, a binocular microscope was used to insure proper 

 orientation for sectioning. Sections of the larvae and pupae 

 were cut from 6 to lO/x in thickness, while those of the embryos 

 were cut 3 and 4/z thick. Heidenhain's iron hematoxylin was 

 used for staining all sections. 



HISTORY OF EMBRYOLOGICAL WORK ON THE LIGHT-ORGANS OF 



INSECTS 



There are, in general, three conflicting views regarding the 

 origin of the light-organs in insects. One view is that they are 

 derived by a prohferation of the hypodermis and hence are ecto- 

 dermal; another, that they are formed from both ectoderm and 

 mesoderm and, lastly, that they are formed from fat-cells and 

 hence are of mesodermal origin. 



Two views were suggested by early workers concerning the 

 possible ectodermal origin of these organs. The one of these 

 that is least generally accepted was advanced by von Kolliker 

 ('57) and Lindemann ('63), who maintained that the structures 

 are nervous in origin. Von Kolliker compared these organs 

 with the electric organs in fishes, which, together with the fact 

 that the light-organs of insects are under the control of the 

 nervous system, led him to conclude that they are of nervous 

 origin. Lindemann considered the organ a definite part of the 

 nervous system. The other of these views was supported by 

 Owsjannikow ('68), Heinemann ('86), Dubois ('98, '13), and 

 Marchal ('11), who upheld the idea that these organs arise from 

 the hjT3odermis by a proliferation of its cells. Owsjannikow 

 considered the organ in the nature of a gland and hence ecto- 

 dermal in origin. Heinemann, who worked on the light-organs 

 of the elaterid beetles, considered that those organs, as well as 

 the light-organs in the Lampjrridae, were derived from the hy- 

 podermis. Marchal was also of the opinion that they are formed 

 from ectoderm. The observations of all these workers, unless 

 it is Dubois, are of little value, as they studied only the adult 

 organs. 



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JOURNAL OF MORPHOLOGT, VOL. 36, NO. 2 



