THE MAXILLARY PALPI. 93 



minations of the nerve are brought into almost immediate 

 contact with the air, being only separated by the extremely 

 thin membrane of which the sacculi are composed ; and likewise 

 from the fact that the antennal nerves are given off from 

 ganglia, next in magnitude and importance to the optic ganglia. 

 Moreover, it appears more than probable that the olfac- 

 tory sense or some modification of it is, if not the dominant 

 sense, certainly only less important than vision to the insect. 

 The third autenual joint is equally developed in both sexes ; 

 but the habits of the male are not sufficiently understood to 

 justify any conclusions which might be drawn from this fact. 



Section XV. The Maxillary Palpi. 

 PLATE III. e., AND PLATE VIII., FIG. 15. 



The minute structure of the maxillary palpi is so like that 

 of the third joint of the antenna that its description naturally 

 follows the description of that organ. The integument of the 

 palpus is covered with short broad curved scales, about l-2000th 

 of an inch in length, as well as by the large hairs with which it 

 bristles. Besides these there are a number of sacculi, about 1,000 

 on each palpus, each opening by a pore in the centre of a collar, 

 like transparent ring, formed by the protoderm. Some of 

 these sacculi are as large as l-3000th of an inch in diameter, 

 with an external opening about I-5000th of an inch in 

 diameter, but others are as small as those of the antenna. 

 They are very closely set about the extremity of the palpus, 

 but are less numerous at its proximal end. The cavity of the 

 palpus is filled with cells, chiefly belonging to the endoderm. 

 A large nerve is distributed to it from the great nerre trunk 



