212 WILLIAM BRODBECK HERMS 



Hence it seems reasonable on the evidence at hand to conclude 

 that because of their different degrees of phototropism C. vomi- 

 toria is of more importance as a household scavenger (or pest, as the 

 case may be), while L. caesar is distinctly a scavenger of the open 

 fields, lake beaches and the like. 



A further inspection of table 7 leads one to conclude, that both 

 species are about equally positive to the larger luminous area, 

 which indicates (if we accept the test as conclusive) that the image 

 forming power of the two species is about equal, with possibly a 

 a i-light advantage in favor of L. caesar. 



It was shown that the eyeless larvae took a straight path be- 

 tween the two lights without turning, while the adults, which pos- 

 sess compound eyes, turned toward the larger luminous field more 

 frequently by 26 to 41 percent (excess over smaller), which indi- 

 cates discrimination. Since the intensity of the two lights was 

 equal the discrimination must be due to the size of the luminous 

 field and the consequent image formed in the eye. Therefore, 

 these experiments afford a test of image forming powers. 



How do the results from the sarcophagid flies agree with those 

 from Vanessa antiope? Cole ('07, pp. 380-382) found 87.2 per 

 cent of the responses of Vanessa were toward the larger light, an 

 excess of 75 per cent of the whole. Though the ratios of the two 

 lights in Cole's experiments (1 :10000) were not the same as those 

 in mine (1 :7500), it seems quite likely that the eyes of the mourn- 

 ing cloak butterfly are better adapted to the formation of images 

 than the eyes of the sarcophagids. The flesh-flies from the nature 

 of their habits are probably more dependent on odors and would 

 necessarily not need image forming eyes of a very perfect character. 

 Observations made by other investigators further justifiy the 

 findings of Cole; e.g. Parker ('03, p. 461) calls attention to the 

 manner in which Vanessa alights with spread wings and is thus 

 found by other individuals of the same species, involving a well 

 developed image-forming power. Also Latter ('04, p. 88) ''once 

 observed a Brimstone butterfly visiting flowers of the Dog violet 

 scattered along a bank, and picking out these flowers to the exclu- 

 sion of all others with great precision, not even approaching other 

 blue flowers that were present." 



