HYMENOPTERA. 755 



head ; the side-pieces of the prothorax overlap the prosternum. 

 The antennae are as a rule simple. The mandibles remain 

 conspicuous and are used for manipulating the wax and for 

 many purposes other than eating. This is especially the case 

 where a fluid pabulum is sucked up the " tongue," which is 

 formed of the elongated first and second maxillae. The palp 

 of the first maxilla is often rudimentary. 



The number of visible segments in the abdomen varies from three 

 to nine, and the abdomen in the female terminates in an ovi- 

 positor or sting which arises from outgrowths on the penultimate 

 and ante-penultimate segments (Fig. 485). These outgrowths 

 are by some regarded as homologous with true limbs. Amongst 

 bees the legs take an active part in the collection of pollen. 

 The wings are usually transparent and in the more typical 

 forms a row of hooks on the anterior border of the posterior 

 wing catch into a raised rim on the hinder edge of the fore- 

 wing so that the two wings on each side are held together, and 

 vibrate as a single membrane. 



The tracheal system as in the Diptera is provided with vesicu- 

 lar swellings along each side of the abdomen. The nervous 

 system tends to show a reduction of the number of ganglia and 

 considerable concen- 

 tration. 



The larvae are cruci- 

 form and always have 

 a distinct head. They 

 are never quite so re- 

 duced as are some of & ^_s- ft 



the DipterOUS mag- Fm 486 _ a Larva of a hum ble bee about to become 



gots, but nevertheless Iffi,. 6 pseud - pupa ^-wj*) , c P u P a ( , 

 the larvae of the 



higher social forms are helpless, white, maggot-like creatures 

 with no legs. The larvae of the saw-flies on the other hand are 

 very like caterpillars and have several pairs of pro-legs in addition 

 to the thoracic legs. 



The appendages and the wings of the pupa are free. The 

 latter either shut up in a cell by the parent, as in Bees, 

 Wasps, etc., or protected by a cocoon formed by the larva. 



Parthenogenesis is of wide occurrence in this Order, and in the 

 Cynipidae it is accompanied by heterogamy, or alternation of 



