COLLEMBOLA OF MINNESOTA 73 



come restless, and move about uneasily seeking for dark corners. 

 Unless considerably disturbed they prefer not to jump, and are 

 not particularly strong leapers when they do. 



The most noticeable and interesting thing about the spe- 

 cies is the dimorphism, probably due to sex. I have not been 

 able to satisfy myself on this point as yet, but Mr. MacGillivray 

 suggests that it is the males that bear the horns and tubercles. 

 They possess a pair of strong, curved horns on very conspicuous 

 tubercles situated at the outer angles of the fourth abdominal 

 segment. These horns project caudo-laterad and somewhat dor- 

 sad. Besides the horns, the males possess variously shaped 

 tubercles upon almost every part of the body surface, most 

 conspicuous and largest on the caudal edge of the segments. 

 Each tubercle is thickly set with short hairs. There seems no 

 doubt that the tubercles are merely modified hairs, for one finds 

 on the same individual nearly all gradations from the thick, stout 

 hair with a very few short hairs at its end to the much swollen 

 tubercles with their haired areas greatly distended. Some of 

 the small tubercles with which the final abdominal segments 

 are thickly set, have the haired surface so much swollen as to 

 form a cap over the rest of the tubercle, giving to the whole a 

 mushroom-like appearance. It appears that the tubercles are 

 haired on one side only, and the swelling of this side causes the 

 opposite (unhaired) side to bend under, as seen in the series of 

 tubercles, figures 8-u, The females possess neither horns nor 

 tubercles, the skin appearing smooth and Abd. IV not widening 

 out laterally. After examining nearly a hundred specimens I 

 have found but one which seems to come between the two. This 

 specimen is without the horns, and has the general build of a 

 female, yet bears some few tubercles, mostly small, on the 

 body. In the male there are tubercles on the antennas and even 

 on the tibiae. This anomalous specimen may possibly be an im- 

 mature male. 



Entomobrya bicolor n. sp. 

 PI. XVI, Fig. 2. 



Dark brown or blue-brown and yellow, appearing yellow 

 and black to the unaided eye in life. More hairy than any other 

 species I have seen. Head and body very dark, with the follow- 



