298 ZOOLOGY 



the long-tongued species which visit tubular flowers. 

 In some of the least specialized bees the tongue is 

 very short and broad, and notched in the middle, 

 indicating its primitively double nature. In others it 

 is daggerlike, and by selecting appropriate species one 

 may arrange a series with successively longer tongues 

 until we come to certain tropical bees in which the 

 tongue is actually longer than the body and when 

 turned backward projects behind like a tail. On each 

 side of the tongue are the four-jointed labial palpi. 

 These palpi or feelers in the lower bees have four 

 similar joints, but as the tongue elongates, so do the 

 two basal joints of these palpi, while the two apical 

 joints remain at the end, still small and unmodified. 

 The maxillce form external sheaths, and these too bear 

 palpi, with the maximum number of six joints. In the 

 higher bees these palpi seem unable to keep up with the 

 elongation of the other mouth parts, and they become 

 reduced to five, four, three, or two joints, or even dis- 

 appear altogether. They follow the law that useless 

 parts tend to become smaller, but usually remain as 

 vestiges. It is also to be noted that, as in so many 

 other cases, the number of parts (as joints of the palpi) 

 may become reduced, but never increased over the 

 primitive number. 



Wings of So, again, in the wings of bees we find specialization 



by reduction. The upper wing of a bee or wasp shows 

 a thickening on the upper margin, called the stigma. 

 This may be large, or almost absent. Just beyond the 

 stigma is an inclosure, bounded by so-called veins, 

 known as the marginal cell. Below the marginal cell 

 are other inclosures, often more or less square, the 

 submarginal cells. The usual number of submarginal 

 cells is three, but there may be only two, and a small 

 parasitic bee has only one. 



