TYRINI 341 



In general the first two palpomeres are relatively stable, the first usually 

 very short, cylindrical, and inconspicuous; the second very long, more or less 

 arcuate, slender basally and more or less inflated apically. The third shows much 

 more variation, being arcuate-pedunculate, obconical, triangular, or spherical. 

 The fourth varies the most, being one of the most labile regions of the tyrine 

 body, as may be seen in the illustrations. Thus we find that in both the tyrine 

 and hamotine types, the degree of variation is in direct proportion to the dis- 

 tality of the palpomere. 



Under the dissecting binoculars I have observed pselaphids feeding upon 

 oribatid mites and small staphylinid larvae, as well as the larval and pupal 

 brood of host ants, and in these cases the maxillary palpi were continually in 

 use, being twirled about and especially the distal palpomere being used to rap- 

 idly, lightly touch the food in a continuous tapping. Such exploratory behavior 

 suggests a sensory function, and the demonstrable secretion of the distal palpo- 

 mere of many tyrines supports this view. Real progress would be achieved by 

 making a study of serial sections of these organs. 



I regard the tyrine type of palpus as primitive and the hamotine type as 

 highly derived. Thus if we assume a fusiform distal palpomere with a simple, 

 acute apex as a hypothetical basis for evolution, the neotropical genera may be 

 arranged as follows: 



A. Development of the tyrine type. 



1. Phalepsus with a very primitive, fusiform distal palpomere. 



2. Development of three tyrine modifications of the distal palpomere, 

 but with the first three palpomeres primitive: 



a. Lethenomus in which the fusiformity is lost and the segment be- 

 comes obconical-pyriform and the internal face, near the apex, becomes pointed 

 and pubescent. 



b. Tyropsis, Neotyrus, Tyrogatunus in which the apex becomes more 

 or less truncate, with an apical palpal cone set within the truncature in the first 

 two genera, and secondly this truncature moves basad over the dorsal face to 

 form a sulcus in the last genus. 



c. Juxtahamotopsis with the shortening of the third and fourth seg- 

 ments, and the development of many subpalpal cones. 



These three lines are quite unrelated to each other. 



B. Development of the hamotine type. 



This appears most feasible from the lower end of 2b {Neotyrus-Tyropsis 

 stock), in which certain tendencies are assumed: the shortening of the long axis 

 of the third palpomere from elongate-pedunculate to triangular; second, loss of 

 fusiformity of the fourth palpomere which involves increasing width and in- 

 creasing basal obliquity; third, the apical truncature of fourth palpomere moves 

 basad over the internal face to form a longitudinal sulcus; fourth, as the sulcus 



