168 WILLIAM BRODBECK HERMS 



I. GENERAL INTRODUCTION 



1. Historical 



Though the blow-flies (including Lucilia caesar) have been 

 the object of study in early times, the first published observations, 

 to the writer's knowledge, relative to the larval reactions to 

 light were given by Pouchet ('72). This writer reports certain 

 observations and experiments by which he demonstrated the 

 sensitiveness of these larvae to light ; he observed that larvae that 

 were feeding in a mass of old hair and other slaughter-house refuse, 

 came to the surface at night and crept back into the mass at day- 

 light, or when artificial light was thrown on them. To prove 

 that heat had no part in the reaction, Pouchet placed a vessel 

 containing water heated to about 80° [C] on top of the heap of 

 refuse, with the result that the larvae did not move away from the 

 vessel as from the light, but on the contrary tended to collect in the 

 vicinity of the warm body. Having satisfied himself experimen- 

 tally that the larvae are sensitive to light, he then set about dis- 

 covering what organs are affected, and also whether the quality 

 and intensity of the light have any effect. Eristalis tenax and 

 Lucilia caesar were used for the investigation and it was shown 

 that the larvae were not only sensitive to light, a fact which 

 Lowne ('90, '92 p. 71) also observed, but that they responded to 

 the direction of the ray, Pouchet moreover showed that the reac- 

 tion to light was immediate. He proposed the term ''Actinaes- 

 thesie" to designate the property which dipterous larvae with- 

 out eyes, but responsive to light possess. By means of this 

 sense they become receptive to the intensity and direction of lumi- 

 nous radiations. Besides discussing the tracks made by the lar- 

 vae, he took up the question of the age at which the larvae begin 

 to show sensitiveness to light and it was shown that they avoided 

 light immediately upon hatching, but that at that time they were 

 not able to react to its direction. This latter reaction grows 

 progressively as the individual gets older but is not fully devel- 

 oped until the larva has completed its growth. Pouchet concludes 

 that actinaesthesia depends upon the ocular buds (the embryonic 

 eyes, so-called), that the light impinging at different angles on the 



