BEETLES 187 



fluid that reaches the surface through small pores. Hicks sup- 

 posed that he detected nerve cells. Meinert is of opinion that 

 the elytra correspond to the teguke of Hymenoptera rather than 

 to the wings of other Insects, but the little evidence that exists is 

 not favourable to this view. The two elytra are usually, in repose, 

 very perfectly fitted together by a complete coadaptation along the 

 middle of the body, so that it is difficult to separate them ; this 

 line of junction is called the suture. There are forms in which 

 the coadaptation is quite imperfect (Malacodermidae) and some 

 in which it does not exist at all (Meloty. The wings proper of 

 beetles correspond to the posterior pair in other Insects, and are 

 much more irregular in nervuration than those of most other In- 

 sects, correlative, it is supposed, with the folding they are subjected 

 to in order to get them beneath the wing-cases. There are large 

 numbers of species, genera, and groups of genera, all the members 

 of which have the wings so much reduced in size as to be quite 

 useless for purposes of flight. These forms are called apterous, 

 though they are not really so, for the elytra (which are really 

 the anterior wings) are present, and even the posterior wings 

 are not truly absent in these cases, though they are sometimes 

 so extremely rudimentary as to elude all but the most careful 

 observation. The number of forms in which the elytra are 

 absent is extremely small ; this condition occurs only in the 

 female sex ; it is usually confined to cases in which the female 

 is larva-like in form ; but in the extraordinary Mediterranean 

 Lamellicorn genus, Packypus, the females are destitute of wings 

 and elytra, though the anterior parts of the body are normally 

 formed : these individuals live underground and rarely or never 

 emerge. When the wings are absent the elytra are frequently 

 soldered ; that is to say, united together along the suture by some 

 sort of secondary exudation ; this union occurs in every degree of 

 firmness, and appears to be variable in the individuals of one 

 species ; probably in accordance with the age of the individual. 

 In most beetles the elytra are not only themselves closely con- 

 nected, but are also very accurately coadapted with the sides of 

 the body, except at the tip. Sometimes a coadaptation occurs 

 between the tips of the elytra and the body, but not at the tip of 

 the latter. In such cases one or more dorsal plates are left ex- 

 posed : the last of such exposed dorsal plates is termed pygidium : 

 a similar plate anterior to the pygidium is called propygidium. 



