486 A. M. Banta 



2. Caecidotea, though at first less rheotactic than Asellus, is 

 persistently rheotactic, whereas the rheotactic response with 

 Asellus is only temporary. 



Photic and Rheotactic Stnuulation 



1. When subjected to the influence of a current of water in a 

 trough the upper end of which is strongly illuminated, both spe- 

 cies, though for a time apparently responding to the rheotactic 

 stimulus alone, soon react principally to the light. 



2. When the upper end of the trough is darkened, Caecidotea 

 more persistently remains within the darkened upper end. 



Food 



1. Caecidotea and Asellus take about the same food, but 

 Asellus eats much live plant tissue with the decaying plant tissue. 



2. Asellus takes in vastly more debris and particles of mineral 

 matter with its food than Caecidotea. 



General Habits 



1. Caecidotea stygia and Asellus communis are not only struc- 

 turally similar, but their habits and reactions to various stimuli 

 are very much alike although there are several minor diff^erences 

 in their reactions. 



2. The cave species is decidedly less sensitive to light than its 

 above-ground relative. 



3. Cave animals do not have need for highly discriminating 

 light-receptive organs. Their movements are well regulated by 

 light-receptive organs which are capable of distinguishing only 

 considerable intensities of illumination, so that when approaching 

 the outlet of subterranean waters their negative response to light 

 restrains them from passing beyond the limits of caves. 



4. The subterranean Caecidotea is clearly very much more 

 sensitive to tactile stimulation than its epigeal relative. 



