322 younial of Comparative Neurology and Psychology. 



orders of succession. By this means his records show the reaction of the animal 

 to each intensity after exposure to each other intensity. This arrangement sug- 

 gests a labor saving way of studying various kinds of previous stimuH upon Hght 

 response. He finds that Cyclops is neutral to artificial lights of low intensity and 

 negative to those of high intensity if it be subjected to them after confinement in 

 darkness. Exposure for some time to light of any intensity makes it negative in all 

 kinds of illumination. Especially interesting is the influence of light upon the geo- 

 tropic response. Under illumination so diffuse as to be non-directive the animals 

 are strongly positive in their geotropism. If light be removed they become negative. 

 EsTERLY concludes that phototropism is of little importance in the diurnal migra- 

 tion in a direct way. Light, however, probably produces some photo-chemical 

 change in the animal, as a result of which positive geotropism occurs during the day. 



Harper's (07) work has to do with the insect larva Corethra. The animal is 

 positively geotropic in strong light whether it come from above or below, and nega- 

 tively geotropic in dim light. It is also distinctly phototactic. It is evident that the 

 chief effect of the light upon migration must be due to its action upon geotropism. 

 Harper thinks that it is likely that while the animal would go down in the day and 

 come to the surface at night obedient to geotropism it would also respond phototrop- 

 ically by collecting in well illuminated areas at whatever level it happened to be 

 swimming. 



There are several extremely interesting and rather lengthy quantitative studies 

 upon the distribution of plankton in various American and European lakes of which 

 a recent example has appeared in the work of Juday ('04). It is not advisable to 

 discuss them here as their interest is chiefly ecological. It may be said, however, 

 of Juday's work that it shows conclusively that light is a very important though 

 by no means the only factor in diurnal migration. It brings to light the fact that the 

 downward migration of plankton begins long before sunrise if not before midnight. 

 The reason of this early departure from the surface is not forthcoming. 



INSECTA. 



In his paper on the light reactions of the pomace fly Drosophila, Carpenter 

 ('05) gives us one of the first general analyses, by laboratory methods, of the light 

 responses of a winged insect. Like many Crustacea, Drosophila is strongly photo- 

 tactic as well as photokinetic. Like Daphnia it will go into any strength of light 

 without reversal. Very great intensity produces not only rapid movement but 

 apparent loss of coordination. By shaking the jar containing the flies they are 

 rendered negatively geotropic. It is a suggestive fact that as in the case of plankton 

 crustaceans light may affect the geotropism while not acting directively itself. Car- 

 penter believes its effect is produced through a stimulating action much like that of 

 the mechanical shaking. 



mollusca. 



Frandsen ('01), MiTSUKURi ('oi), Walter (06) and Bohn have given more 

 or less attention to the behavior of gasteropod mollusks toward light within the 

 period of this review. It would not be profitable to consider their papers since not 

 only has there been a lack of an extended recent study of the group but there is 

 also investigation under way upon their light reactions. 



