INTROnUCTIOX. XXI 



confound with the male intromittent organ ; it is really (as Dr. Sharp, 

 who has studied the character more than any other author, informs me) a 

 segment of the body withdrawn into the interior and variously and 

 profounclly modified for the purposes of fertilization ; in some cases it 

 appears to consist of more than one segment ; in the Dytiscidai it is 

 arranged so as perfectly to keep out water during coupling ; it is not 

 ])ropcrly speaking part of the organs of generation, but is a highly 

 modified secondary sexual apparatus, which has nothing homo- 

 logous with it in the Vertehrata ; it is of extreme variety in the 

 Coleoptera, and appears not to be absolutely confined to the male, for 

 where the number of external segments in the male and female is the 

 same, there will be found in the female an internal (usually chiefly 

 membranous) segment homologous with the male cedeagus : in the 

 Sta]^bylinidpe the segment preceding the oedcagus is also more or less 

 modi lied or retractile. 



Occasionally the modifications of the organs of generation are very 

 curious : the female of Cehrio r/ir/as, for instance, usually lives below the 

 surface of the ground, above which, at the period of coupling, it protrudes 

 a long horny tube, the extremity containing the organs of generation ; at 

 this time the males may be found searching eagerly for the females ; 

 after coupling the same organ is employed to introdiice the eggs to a 

 proper depth under ground (v. "Westwood, Classif. i. 245). 



The difference in structure of the sexes with a view to generation, 

 especially as regards the development of the tarsi, femora, &c., in male, 

 and the sculpture of the upper surface of the female are in many cases of 

 the greatest interest ; the antenn;e also are often largely modified as in 

 certain Elateridae, INfeloe, &c. ; these diflerences, however, belong ratlier 

 to external structure, and will be more fully alluded to under the several 

 genera. 



External Structure. 



As it is chiefly on the external structure that descriptions of Coleop- 

 tera are at present founded, it is of the first importance that till students 

 of the order should make themselves thoroughly acquainted with it and 

 Avith the terms employed in describing it ; the details, therefoi'c, of the 

 complicated external skeleton, mouth parts or trophi, antenna*, legs, &c., 

 must l)e fully explained in any work like the present, and will therefore 

 for convenience sake lie treated of under three separate headings. 



1st. The head, including the mouth organs, antenmie, and eyes ; 2nd. 

 Tlu>. thorax, including its appendages, the wings, and the legs ; and 

 3rd. The abdomen or hind-body, by which latter term it is generally 

 now known in descriptions of the Staphylinidte. 



The Head. 



The head varies very greatly in form : as a rule the hinder portion is 



not nnrrowpil and is sim|)ly inserted into tlic fniut of the tliorax, to wliicli 



