AMPHIPODA— GAMMARID^. 79 



attacked and fed upon the smaller. It appears to breed at all seasons, 

 old with young- in the brood pouch being found throughout the year. 



C. gracilis is found in some abundance in the Donaldson Caves at 

 Mitchell. Bollman (Packard, 1888, 36) and later Blatchley (1896, 206) 

 reported it from Mayfield's, and Blatchley (1896, 206) found it it Eller's 

 and Donnchue's caves. It is common in southern Illinois and in central 

 Indiana. I have found it to be common and very abundant about 

 Blooming-ton and Mitchell, Indiana. 



The C. gracilis found in Mayfield's Cave has well-developed and 

 distinctly pigmented eyes, but differs from the outside form of this 

 region, (1) in the total lack of pigment, except in the eyes, the out- 

 side form being rather dark, and (2) in the larger size, the largest 

 from outside measuring 13 mm. and the largest from the cave more 

 than 18 mm. in length. Three of the largest ones from the cave meas- 

 ure 18.4, 18.2, and 18.2 mm. respectively; three of the largest from 

 outside, 12.5, 13.1 and 11.8 mm. respectively. I have kept individuals 

 of this species in the laboratory in the light as long* as 8 months, to 

 test the possible effect of light upon the development of dark pigment. 

 Not one of the many young liberated in the light by females with young 

 in the brood pouch when collected (I have not had them to breed during 

 captivity) nor one of the old ones, showed any indication of taking on 

 color. A careful detailed study of a series of this variety compared 

 with a series of C. gracilis from outside of caves has not been made. 

 Such a study will probably reveal other differences between the two 

 forms. 



W. P. Hay (1896, 206) says of the occurrence of this species in caves: 



The animal is not one given to life in such situations, and I am of the opinion 

 they are to be regarded as accidental visitors only, having been washed by heavy 

 rains into the cave streams, from which they have been unable to make their escape. 



Blatchley (1896, 206) says: 



From the nature of the stream in the cave (Mayfield's) I do not think it is possi- 

 ble for it to escape, and facilities are, therefore, excellent for a future study of the 

 length of time necessary to bring about organic changes due to cave environment. 



After having carefully laid off the course of the cave stream in 

 Mayfield's Cave under ground and plotted it above ground, I am con- 

 vinced that the cave stream has no origin above ground or that at most 

 it may receive water from only a sink-hole ordinarily dry. Since there 

 is no above-ground pool or counterpart of the under-ground stream 

 from which this species could be swept into the cave, it is impossible 

 for it to have been carried into the cave by heavy floods. After heavy 

 rains the cave is more or less flushed, due to sink-holes and percolating 

 water, and during a time of phenomenally high waters in April, 1904, 

 the whole cave was nearly completely filled with water. Such a flood, 



