THE FAT BODIES AND DUCTLESS O LANDS. 29 



the edges of the valves of the thoracic trachea?,* perhaps also of 

 a plate in the forehead, which covers a membranous cavity in that 

 part. The sound is attended with a violent vibration of the whole 

 thorax, probably chiefly produced by the rapid contraction of 

 the dorsal muscles. The vibration of the wings may, and probably 

 iloes, give rise to a peculiar note ; but owing to their movement 

 being always attended with vibrations of the thorax, it is difficult 

 to determine how much is due to them. Another note is pro- 

 duced by the rubbing of the head against the thorax. | 



Section IX. The Fat Bodies and Ductless Glands. 



Two dissimilar structures have been confounded under the 

 term fat bodies, the omenta of the larva, and the ductless glands 

 of the imago. 



The former consist of plicated cellular expansions formed 

 of large flat cells of hexagonal outline, adhering to each other by 

 their edges, which are firmly attached to the lateral trachea? 

 of the larva, in which a store ef elaborated nutriment is laid up 

 for the development of the pupa. 



The fat bodies or ductless glands of the imago consist of closed 

 follicles, arranged upon the tracheae in an arborescent manner ; 

 the follicles themselves are composed of structureless membrane, 

 and contain peculiar nucleated corpuscles, nuclei, and granules ; 

 in the mature insect they are often loaded with oil globules. From 



* Dr. H. Landois, Die Ton und Stimmaparate der Insecten, Kolliker 

 Zeitchrift, Band. 17, 105. 



t Dr. H. Landois and W. Thelen, Der Tracheenverschluss bei den 

 Jnsecten. ibid. Band 17, 187. 



