1 86 COLEOPTERA 



CHAP. 



dorsal and ventral plates is due to two facts ; 1, that the 

 hind coxae have a great and complex development, so that they 

 conceal the true base of the venter, which, moreover, remains 

 membranous to a greater or less extent, and thus allows much 

 mobility, and at the same time a very accurate coadaptation 

 between the hard parts of the venter and the metasternum x ; 2, 

 that the terminal segments are withdrawn into the interior of 

 the body, and are correspondingly much modified, the modifica- 

 tion being greater in the case of the ventral than in that of the 

 dorsal plates. The anatomy of the parts of the abdomen that 

 are not externally visible has not been adequately studied by 

 coleopterists, but Yerhoeff has inaugurated a careful study of 

 the comparative anatomy of the terminal segments 2 ; unfor- 

 tunately, however, he has not so thoroughly studied the modifi- 

 cations at the base, and as it is not clear that these are so 

 uniform as he has taken for granted, it is possible that his num- 

 bering of the segments may have to be in some cases modified. 

 The retracted plates or segments are so intimately connected 

 with the internal copulatory organs that it is no easy matter to 

 interpret them. For the nomenclature of these parts we must 

 refer the student to Yerhoeff' s later works. He considers the 

 abdomen as composed of ten segments, the dorsal plates being 

 demonstrable, while the tenth ventral plate is usually absent. 

 The anal orifice is placed immediately beneath the tenth dorsal 

 plate, and above the genital orifice, which lies behind and above 

 the ninth ventral plate. Peytoureau admits a diversity in both 

 the number of segments and the position of the orifice. These 

 studies in comparative anatomy are surrounded with difficulties, 

 and no morphological conclusions based on them can be con- 

 sidered as final until they have been confirmed by observation 

 of the development of the parts. 



The elytra or wing-cases frequently have a remarkable 

 sculpture, the use of which is unknown. According to Hofbauer 

 there are between the outer and inner layers, glands secreting a 



1 An interesting exception occurs in the Malacodermidae, where this coadaptation 

 is wanting, or is imperfect ; they are frequently considered to be the most primitive 

 of existing beetles. 



2 In a series of memoirs in various German periodicals during the last five or six 

 years (see especially Deutsche cut. Zc.it. 1893 and 1894, also subsequent years of 

 Arch. Nat-urges.). It should be noticed that in the course of his studies Yerhoeff 

 has modified some of his earlier views. 



