Insects^ and its Functions during Flight. 395 



divided by them into an external and internal portion,) and at 

 others with this base and the dorsum by the intervention of small 

 bones. In the Coleoptera the supports of the elytra are denomi- 

 nated anterior or scutellar clavicles ; and the term of fulcral 

 plates is given to the scales to which the supports of the wings 

 are affixed. 



From the nature of its functions, the wing-bearing trunk re- 

 quires to be alternately dilated and contracted during flight ; and 

 in consequence of this necessity the several pieces of which its 

 dorsal portion is composed are loosely connected together only 

 by ligaments varying in number and in elasticity. The most con- 

 siderable of these pieces is called preeminently the dorsum ; with 

 this the wings are articulated, and to this the principal muscles of 

 flight are attached, except in the Libellulae, in which these 

 muscles are inserted directly into the wing. There exists a dis- 

 tinct dorsum for each pair of wings, the size of which is con- 

 stantly proportionate to the importance of the wings, and to the 

 power of the muscles of flight which are affixed to it. It is con- 

 vex above and concave beneath, and is frequently divided by a 

 longitudinal line into two equal and similar parts. Its margins 

 are always curved more or less downwards ; and the lateral ones 

 are furnished with apophyses, termed humeral, by which they are 

 articulated with the internal side of the base of the wings, either 

 immediately, or by the intervention of small bones. The other 

 angular portions of its margins serve for its articulation with other 

 contiguous parts. 



In the Coleoptera the body of the dorsum is covered during rest 

 by the wings and the elytra ; and its anterior portion, contracted 

 into the form of a neck, and covered above by a simple membrane, 

 is hidden under the scutellum with which it is articulated. It is 

 terminated in front by a transverse and nearly vertical half sep- 

 tum, the pra^dorsum or cervical septum ; into which are inserted 

 the anterior extremities of the dorsal muscles, which in the greater 

 number of the other orders are attached to tlie fore part of a con- 

 siderable portion of the middle third of tlie dorsum. 



In the Acrydia the anterior portion of the dorsum does not be- 

 come at all smaller for the purpose of being inserted into the pro- 



