8 INTRODUCTION. 



There are as a general rule six visible ventral segments, but the 

 intermediate articulations permit of little movement and may be 

 completely soldered and even obliterated. The spiracles number 

 two on each side of the thorax and seven on each side of the 

 abdomen, the latter being entirely situated in the connective 

 membranes in the Laparostict divison of the Scarab.tid.i: and in 

 part in the chitinous rings in the Pleurostict division. 



An important characteristic of the Lamellicornia both in the 

 mature and larval states is found in the concentration in the 

 anterior part of the body of the central nervous system. In a 

 typical insect this consists of a brain and a median ventral 

 chord bearing a series of ganglia corresponding more or less 

 exactly with the segments, one being in the head, three in tlie 

 thorax and usually eight in the abdomen. In the Scakae^id-E two 

 or (sometimes) all of the thoracic and all the abdominal ganglia are 

 found collected into a single mass between the first and second 

 thoracic segments, the abdomen being supplied only by the lateral 

 nerve branches given off in pairs from the posterior part of this 

 mass. In the Lucanid larva the ganglia are distinct and form a 

 chain, but in the adult beetles, although not massed together as in 

 the ScAKAB.EiD.^, they are reduced in number and do not extend into 

 the abdominal region.* In the remaining Lamellicorn family, 

 Passalid.e, no part of the internal anatomy has hitherto been 

 described and the condition of the central nervous system of larva 

 and imago is shown in the accompanying diagram. In the larva the 

 ganglia are all distinct and distant, the first three placed one in 

 each thoracic segment, the fourth also accompanying the metathorax, 

 while the first seven abdominal segments contain one each. In the 

 imago a striking change takes place. The cephalic and first 

 thoracic ganglia alone remain distinct, and all succeeding ones are 

 massed together in a short rod-like body the hinder end of which 

 reaches no farther than the point of origin of the second pair 

 of legs. A pair of strong nerve fibres run from the extremity of 

 this body into the abdomen and several other pairs arising before 

 the extremity and running parallel with them indicate ganglia no 

 longer separately distinguishable. Thus the Passalid larva, which 

 externally has the most abnormal organisation among Lamellicornia, 

 is entirely primitive in its nervous system, while the imago, which 

 also is of a highly peculiar and isolated form, is in that respect 

 almost identical with the Scarab.'EID.t:. 



The internal anatomy of the Lamellicornia, as represented by 

 the common European Cockchafer, MdoJontha vulijar'm, was the 

 subject of the elaborately illustrated Monograph of Straus- 

 Durckheim, published in 1828, " Considerations genorales sur 

 I'Anatomie Comparative des Animaux articules," and later 

 investigations have been collated by Professor Kolbe in his 

 " Einfiihrung in die Kenntniss der Insecten," 1893. The alimen- 

 tary canal has been studied in many representative genera by 



* L6on Dufour, Ann. Sci.Nat. (2) xviii. 1842, p. 162. 



