196 CHARLES HARLAN ABBOTT 



In the experiments of Torrey and Hays the source of illumi- 

 nation was a Mazda bulb held near the animal. No attempt was 

 made to measure the intensity, but apparently all the work was 

 done with rather high intensities. 



Many of the questions which arise with regard to the hght 

 reactions of land isopods are not answered by either of the 

 papers just referred to. The present study is an attempt to 

 gain a more thorough understanding of the reaction of land 

 isopods to light, in order to interpret the ecological significance 

 of the behavior. 



III. MATERIAL 



The common species of land isopods belong to the superfamily 

 Oniscoidea and to the family Oniscidae. They are favorable for 

 experimental work because they are abundant, are generalized 

 in their mode of life, and are suited to life in a laboratory. The 

 species Oniscus asellus Linn, was used chiefly for the study, but 

 for comparative purposes two other common species, Porcellio 

 rathkei Brandt and PorcelHo scaber Latreille, were also tested 

 in many of the experiments. Complete descriptions of these 

 species are found in Richardson's Monograph (Richardson, '05), 

 and it is not necessary to repeat them here. Various points in 

 the description important from an environmental standpoint, 

 particularly differences between the genera, are given in suc- 

 ceeding pages. 



As sowbugs live normally under almost any object that fur- 

 nishes concealment together with a certain degree of moisture, 

 and as they frequently invade houses, it is not difficult to du- 

 phcate their natural surroundings in the laboratory. They were 

 kept in round glass dishes, containing earth, dry leaves, and 

 bark, and covered to prevent evaporation. To allow for pos- 

 sible results of differences in temperature, some were placed in 

 ordinary heated rooms, while others were left out of doors in 

 wooden boxes. Attempts to keep them alive outside the building 

 during the winter months were, however, unsuccessful. Other- 

 wise many of them lived an apparently normal life for several 

 months in the various habitats, and some which were kept in a 

 warm room produced broods of young in December. 



