PODOPTHALMATA ASTACID^E. 75 



cent of the length of the body. Hence the Mayfield's Cave individuals 

 have antennae 11.89 per cent longer than individuals of the same species 

 from outside of caves in the immediate vicinity. This means that 

 Cambarus bartoni in Mayfield's Cave has acquired a constant character 

 different from C. bartoni above ground in the same locality. 



There is also a noticeable difference in pigmentation in the two series, 

 the cave series being lighter. This difference in pigmentation is not 

 great, but it is fairly constant. There was no noticeable difference in the 

 size of the eyes nor in any other characters, although the rostrum length 

 seemed possibly a little greater in the cave specimens. These changes in 

 Cambarus bartoni have occured while the individuals might have followed 

 the course of the stream and escaped. Evidently individuals of this 

 species have voluntarily and by preference remained in the cave, where 

 they have become modified so that a local race has been formed. 



A third series of 35 specimens from the stream which runs between 

 the Twin Caves, and from about the mouths and within the Twin and 

 Donaldson's Spring caves, was measured. This series had antennae 

 100.95 per cent the length of the body or 8.29 per cent longer than the 

 average of above-ground forms about Bloomington. It seems quite 

 possible that in this case the increase in length of the antennae is due 

 to the influence of a partial cave life. 



In C. bartoni tenebrosus Hay the antennae are longer than in typical 

 C. bartoni. The other distinguishing characters of C. bartoni tenebrosus 

 do not exist in specimens from Mayfield's Cave. 



The possibility of a correlation in certain cases between life in caves 

 and increased size suggests itself. Unfortunately the small series of 

 C. bartoni from Mayfield's Cave contained only individuals of aver- 

 age size even for typical C. bartoni, but the individuals from Mitchell 

 often reach more than 100 mm. in length, while individuals of C. bartoni 

 tenebrosus more than 100 mm. in length are common, and I have one 

 which measures 135 mm. I have never seen C. bartoni, living away 

 from caves, over 84 mm. in length; 70 mm. in length is the usual maxi- 

 mum attained. 



This same increase in size is noted in Crangonyx gracilis from May- 

 field's Cave as compared with the same species outside of caves. The 

 greater size attained by these two species when living in caves is 

 remarkable in view of the apparent scarcity and difficulty of obtaining 

 food in caves. Possibly the scarcity of food is compensated for by the 

 scarcity of enemies and consequent longevity of cave inhabitants. 



