224 WILLIAM BRODBECK HERMS 



the latter is distinctly a scavenger of the open fields, lake beaches 

 and like situations. 



2 1 . The adults when tested for opposing fields of different areas 

 but with like intensity react positively to the larger area of light. 



22. The image forming powers of the eyes of the adults are 

 about equal for the two species, and relatively well developed. 



23. The path of the individual larvae is largely predetermined 

 by the direction of the rays, but is greatly influenced by intensity. 



24. The after-effects of light stimulation are an important modi- 

 fying or obscuring factor in behavior, as is also mechanical stimu- 

 lation. 



25. In the process of phototaxis after stimulation, at least two 

 distinct steps should be recognized, first, orientation, leading to, 

 second, locomotion. 



26. In low light intensities these larvae orient by an indirect 

 method, which may be termed "trial and error" or ''random 

 movements;" in higher intensities the larvae orient by a direct 

 method. 



27. There is a gradual transition from one method to the other; 

 therefore it seems preferable in reference to the organisms in 

 question to designate this as a combination method of orientation, 

 uniting the two general schemes in one. 



28. The locomotion of the organisms away from the source of 

 light is governed almost exclusively by the influence of symmetri- 

 cal stimulation on a bilateral animal, and consequently falls 

 under the definition of a tropism. 



29. The negatively phototactic reaction of sarcophagid fly- 

 larvae is highly adaptive. 



BIBLIOGRAPHY 



Adams, G. P. 1903 On the negative and positive phototropism of the earthworm 

 Allolobophora foctida (Sav.) as determined by light of different inten- 

 sities. Amer. Jour. Physiol., vol. 9, no. 1, pp. 26-34. 



CoHN, F. 1853 Ueber eine neue Gattung aus der Familie der Volvocinen. Zeit- 

 schr. f. wiss. Zool., Bd. 4, Heft 1, pp. 77—116, Taf. 6, Fig. 1-21. 



1866 Ueber die Gesetze der mikroskopischen Pflanzen und Thiere unter 

 Einfluss des Lichtes. Hedwigia, Bd. 5, no. 11, pp. 161-166. 



