4 EXTERNAL ANATOMY OF INSECTS. 



The present paper, though but a portion of a larger work, 

 and relating only to one segment out of the thirteen, is in itself 

 complete, inasmuch as it contains all that will be said con- 

 cerning the head. Permit me, further, to premise that the 

 proposed nomenclature and descriptions have reference solely 

 to the hexapods ; the organs described appear throughout the 

 annulate kingdom of animals, but under widely different cir- 

 cumstances and forms. 



I beg to thank the Society for permitting this paper to be 

 read, after I had reserved the right of publication in another 

 channel ; a degree of liberality which, if persevered in, will 

 ensure an overflow of communications. 



It appears scarcely to admit of a doubt, that the head of an 

 insect is composed of four distinct portions. That the por- 

 tions of the head are merely sections, appears to me consistent 

 with the general harmony of Nature." The second segment 

 in the locust tribes, and the third segment in the bee tribes, 

 present to the inquirer a quadruple division by far more mani- 

 fest. You will however remark, and it is of no mean impor- 

 tance, that, while the portions of the second, third, and following 

 segments, are united by suture, those of the head have a freely 

 moveable articulation. That the portions of the head are 

 segments, is argued from the circumstance, that those organs 

 which in one group are employed for manducation, in another 

 serve solely for progression. When this is the case, the organs 

 thus modified differ in no material characters from those of the 

 second, third, and fourth segments. Consequently, it is said, 

 that by their increase of importance to that of true organs of 

 locomotion, they also raise the portions which bear them to 

 an importance equal to that of those portions which uniformly 

 bear such organs. 



These changes in the uses to which organs are applied we 

 frequently detect in progress in intervening groups. They 

 afford the most obvious distinguishing characters. A man 

 is termed a biped ; a horse, a quadruped ; and not in- 

 correctly : yet the number of limbs in each is the same. 

 In man, the first pair of limbs is essential to feeding ; in 



« The segments of tlie head, which are sometimes three, but typically four, 

 are therefore of course only to be considered as secondary. — MacLeay, 



