STUUCTURE OF INSECTS. 2.01 



cles they enclose : for since the surftices which 

 receive, as well as those which are received, are 

 segments of spheroids, this structure admits of a 

 twisting motion ; and also the latter segment may 

 be pushed more or less into the cavity of the former, 

 either generally, or on one side. 



Each segment, besides being separate from the 

 rest, is farther divided into an upper, or dorsal, and 

 a lower, or ventral portion ; each portion having 

 the form of a semicircle, or rather of an arch of a 

 circle. These are connected at the sides by a liga- 

 mentous band, which runs the whole length of the 

 abdomen. Great advantage results from this divi- 

 sion of the circles, allowing of the upper and lower 

 portions of the abdominal covering being at one 

 time separated, and at another brought nearer toge- 

 ther : for thus the cavity is cajDable of being en- 

 larged or contracted in its dimensions, and adapted 

 to the variable bulk of its contents. It is deserving 

 of notice that, during the process of transformation, 

 some of the abdominal segments, which are present 

 in the larva, disappear entirely, or leave only im- 

 perfect traces of their former existence. Sometimes 

 the posterior segments become so exceedingly 

 contracted in their diameter as to give rise to the 

 appearance of a tail : this is exemplified in the 

 Panorpa, the tail of which terminates in a kind of 

 forceps, or pincers. 



The junction of the abdomen with the trunk is 

 effected in various ways. In all the Coleoptera, it 

 is united by the whole margin of its base, without 

 having a narrower part : in other tribes there is a 

 visible diminution of diameter, forming a groove all 

 round, or an incision, as it is technically termed. 



