4 HYMENOPTERA ACULEATA. 



at the head of the lusecta. Their economic and often 

 social instincts tend to place them in this position, and 

 their right to it is supported by their wonderfully specialized 

 structure, the very strongly defined regional constrictions 

 and the highly cephalized imago. 



In the arrangement of the families I have followed the 

 old plan, as it is quite impossible to get a satisfactory 

 linear arrangement, and therefore I have not thought it 

 worth while to disturb the existing one of our lists. 



Fossil Hijmenoptera — The oldest known representatives 

 of this order have been obtained from the Solenhofen 

 State of Bavaria and the Purbecks of this country, both 

 belonging to the Upper Oolite (Secondary Period), but the 

 Hijmenoptera do not appear to have been common and 

 generally distributed until towards the middle of the 

 Tertiary Period. 



The remains of Hymenoptera are not uncommon in the 

 middle and upper Eocene and the lower, middle and upper 

 Miocene. In certain strata of middle Miocene age Professor 

 Heer found the Hymenoptera more numerously represented 

 than any other order of insects. 



Internal Anatomy. 

 Digestive System. — The food passes through a groove 

 at the back of the labium into an enlarged chamber which 

 opens into the oral cavity, thence through the pharynx into 

 the oesophagus, which runs as a narrow tube through the 

 thorax, opening out at the base of the abdomen into an 

 enlargement called the first stomach, honey sac, or crop. 

 At the posterior end of this stomach is a constriction, or kind 

 of mouth corresponding to the gizzard, which can be 

 opened to let the food pass into the chyle stomach, or can 

 be kept clo; ed, eg as to allow the contents of the crop to be 

 regurgitated. Leon Dufour says that in the Crabronidie 

 there exists a lateral stomach or pouch leading out of the 

 cesophagus, sometimes on the left hand side and sometimes 



