XX INTRODUCTION. 



OTHER STRUCTURES. 



Besides the parts of the body above described, there are certain 

 structures occasionally seen, which, from being used for the dis- 

 crimination of genera, need our attention. 



Stridulating organs, or organs for producing sound, exist in 

 various families, and consist of finely wrinkled surfaces, frequently 

 with a pearly lustre ; the sound is produced by friction with some 

 other part in the neighborhood of these stridulating surfaces. 

 The situation of these organs is inconstant ; thus among the Sca- 

 rabseidas they are found in Trox, on the ascending portion of the 

 first ventral segments ; in Strategus, on the propygidium, and in 

 Ligyrus on the inner surface of the elytra. 



Extensible membranous vesicles are observed in one tribe of 

 the family Malachidae ; there are two pairs, one proceeding from 

 a fissure beneath the anterior angles of the prothorax ; the other 

 pair emerging outside, and anterior to the hind coxae. 



The above sketch of the external anatomy of Coleopterous in- 

 sects contains all that is necessary to enable the student to com- 

 prehend the following pages, and in order to facilitate the deter- 

 mination of the family to which any given species must be referred, 

 I will now attempt to display the relations, partly natural and 

 partly empirical, between the different families recognized in our 

 fauna.* 



This synoptic table of families must, in the present state of 

 science, be to a considerable extent artificial, for it is unwise to 

 suppose that in an animal which passes through a complete meta- 

 morphosis, all the highest relations and analogies can be exhi- 

 bited in any single phase of its development. And although the 

 structure of the perfect insect enables us to refer the species to 

 its proper family, yet in grouping the families together, some 

 reference must be had to the characters seen in the development 

 of the animal. Such information is at present too vague to be 

 of service in the higher investigations of science, and for this 



* For the purpose of illustrating to the student modifications of structure 

 used in the tables of this work, I add the following wood-cuts illustratiug 



