370 



Ad fig. 4. 



In the present treatise the measures employed are al- 

 ways relative, never absolute; never e, g. millimeter. All 

 proportions of length and breadth are referred to the length 

 of a special line, the basal line of the mandible in the ani- 

 mal under examination : this line, then, is taken as the unity 

 of measure. In this way, individual measure, originating in 

 nutrition, etc., are avoided and the measures given will be 

 common to all grown individuals of the same species. The 

 basal line of the mandible (be = 1) is the direct line between 

 the dorsal place of articulation of the mandible and the 

 place of attachment of penicillus (or corresponding place in 

 those species where penicillus is wanting). The basal line 

 of the mandible has been selected as a unity for the prac- 

 tical reason, that it is a line of a suitable dimension in an 

 organ that is seldom damaged owing to its strength. More- 

 over, the very varying structure of the mandibles in the 

 different genera is best expressed by this method of measu- 

 ring, and, further, the structure of the mandible characterizes 

 very much the carnivorous or herbivorous nature of the 

 Carabid-larvæ. If the longitudinal line of the mandible (ac) 

 is long in proportion to the basal line, the point of the 

 mandible is moved with great rapidity, but with no great 

 force. Such a condition will be extremely usefull to genera, 

 to Avhom it is necessary to seize their prey with rapidity. 

 On the contrary, a long basal line, and a proportionately 

 short longitudinal line will produce an energetical, though 

 not very rapid bite. Such is the case with the herbivorous 

 larvæ (e. g. Zabrus). A relatively long longitudinal line, 

 and a short distance from the dorsal articulation of the 

 mandible to the top of the retinacle gives at the same time 

 a very rapid movement of the point of the mandible, and 

 a rather slow, very vigorous bite with the retinacle (e. g. 

 Carabus). As a rule, the nasale is more or less developed 

 according to the greater or lesser slenderness of the man- 

 dible and of the elevation of the retinacle above the basal 

 line, and as the retinacle by the plurality of the Carabid- 



