THE PHOTIC REACTIONS OF SARCOPHAGID FLIES 171 



"In the larva of the blow-fly the optic disc (Lowne, '93-95, 

 p. 545) is connected with the central nervous system by the optic 

 stalk, Weismann's 'Nervenstiel,' so that it has the form of a mush- 

 room, the optic stalk forming its stem. The relation of the optic 

 stalk with the central nervous system, indicates undoubtedly 

 that it is a rudimentary optic nerve; it consists chiefly of neuro- 

 blastic cells and their processes, and exhibits a distinct central 

 cavity. It expands beneath the optic disc, and may represent a 

 rudimentary retina : and it is covered by a thin layer of parablastic 

 cells, its peritoneal covering. In this stage the eye disc differs in 

 no respect from the other imaginal discs, so that there is no reason 

 to suppose that its nervous stalk possesses any functional activity 

 as a nerve of sight. The disc is neither pigmented nor has it any 

 special end organs." 



The "great hooks" of the larva are described by Lowne ('90- 

 92, pp. 40-41) as "uncinate processes of the cuticular layer of the 

 integument." "When at rest they are retracted within special 

 cavities in the maxillae, which do not communicate with the 

 mouth. They are the retractile claws of the maxillae. 



They are used as organs of locomotion and probably assist in 

 the disintegration of the flesh in which the larva burrows." 



3. The natural history of the sarcophagid flies 



The principal interest in members of this group at first centered 

 on their usefulness as scavengers of the Lake Erie beach debris 

 which is composed largely of dead fish washed up periodically in 

 large numbers by the surf. (Herms, '07, p. 74). Observations 

 were carried on during the summer months (July and August) 

 at the Lake Laboratory,^ Sandusky, Ohio, for five successive 

 seasons and during the autumn and winter months of 1907-08 

 at the Zoological Laboratory of the Museum of Comparative 



- It is a pleasure at this time to acknowledge my indebtedness to Professor 

 HerVjert Osborn, Director of the Ohio State University Lake Laboratory for the 

 facilities afforded by the Laboratory and for the kind advice given during the pro- 

 gress of this and earlier studies on these animals. 



