Reactions of Isopods to Light 247 



Asellus communis Say. The latter occurs not only in the cave 

 regions of the middle west, but also in the vicinity of Cambridge, 

 Mass. The Caecidotea stygia were obtained from Mayfield's 

 cave near Bloomington, Ind., and from the caves on the Indiana 

 University Experimental Farm at Mitchell, Ind. For collecting 

 and forwarding much of this material lam indebted to the 

 kindness of Drs. Charles Zeleny and W. L. Hahn of Indiana 

 University. 



Caecidotea stygia Packard is a white, eyeless species. It seems 

 to occur rather generally in subterranean w^aters throughout the 

 Ohio Valley (cf. Banta '07, pp. 76-77). It has been found in wells, 

 in most of the caves of the Ohio Valley, and in tile drains in Illi- 

 nois (Forbes '76, p. 13). I have found it also above ground near 

 Bloomington, Ind., in a spring and its stream and likewise 

 under leaves in a sheltered ravine. W. L. Hahn informs me that 

 at Donaldson's Cave near Mitchell, Ind., it occurs under stones in 

 the cave stream outside the mouth of the cave. When found out- 

 side of caves it has been taken from under stones or dead leaves in 

 waters closely associated with subterranean waters. Within caves, 

 "It is often found along the edge of the pools or in the shallow 

 parts of the streams .... More usually, however, it is 

 found under stones in the water Caecidotea stygia is 



a weak species. It can not swim and usually crawls very slowly. 

 It is nearly helpless out of water, its weak legs bemg scarcely able 

 to push it along" (Banta '07, p. 76). 



Asellus communis Say is the common fresh-water isopod. It 

 is distributed, according to Miss Richardson ('05, p. 420), who 

 gives the localities by states, from Massachusetts and Pennsyl- 

 vania on the east to Michigan, Illinois and Mississippi on the west. 

 Near Cambridge it is extremely abundant in many ponds and 

 small streams. It is a more active species than Caecidotea, and 

 is usually found on the substratum, under stones or among dead 

 leaves or crawling about and burying itself in the loose debris scat- 

 tered there. Sometimes, however, it is seen climbing about over 

 Ceratophyllum or other water plants, though it is most abundant 

 in the more secluded situations. Occasionally it appears where the 

 current is fairly strong; more generally it is to be met in fairly 

 quiet waters or even in stagnant pools. 



