496 HYMENOPTERA 



culate bodies of the supra-oesophageal ganglion are considered to 

 be in their development correlative with that of the intelligence 

 or instinct. In the workers of the social Hymenoptera these 

 bodies are very large, while in the males and females they are 

 small. The workers and females of Bombus have six abdominal 

 ganglia, while the males have only five ; and the worker of the 

 honey-bee has five abdominal ganglia, while the male and the 

 queen-bee have but four. In the leaf-cutting bee (Ifegachile) the 

 male has four abdominal ganglia and the female five, and in the 

 wasps the workers have five, the males and females six. The 

 nervous system in the larvae shows but little difference between 

 the ganglia, which are thirteen in number, eight being abdominal. 

 In the embryo of the bee Kowalewsky has observed seventeen 

 ganglia. The changes that take place from the embryonic 

 to the imago condition are therefore directed to the reduction 

 in number of the ganglia, which is accomplished by the 

 fusion of some of them. In the adult Hymenopterous Insect it 

 would appear that the first abdominal ganglion is always joined 

 with the last thoracic. 



Sub-Orders. — The distinction in the form of the abdominal 

 articulation, previously alluded to (p. 492, Fig. 336, A, B), 

 divides the Hymenoptera into two great sub-Orders, the members 

 of which are very different in their habits and life-histories. 

 The Sessiliventres are plant-eaters ; their larvae (Fig. 343, A) are 

 provided with legs, and are able to procure their vegetable food 

 for themselves. The larvae of the Petiolata are maggot-like 

 and helpless, and are dependent for food on supplies afforded 

 them by their parents or companions. It is said by Dewitz that 

 although the larvae of the Petiolata appear to be legless, there are 

 thoracic legs within the body. The metamorphosis, so far as it 

 is known, and the early life-history of the Sessiliventres are very 

 similar to those of Ijutterflies and moths, except that the pupa is 

 soft and has no hard external skin. A few of these plant-eating 

 Sessiliventres become carnivorous in the perfect state — a change 

 of habit that is most unusual in Insects, though the reverse 

 occurrence is common. The larvae of the Petiolata exhibit, in 

 the cases that have been examined, the pecu.liarity that the 

 alimentary canal has not any outlet posteriorly until the ter- 

 mination of the larval stage of existence is approaching. In 

 some cases there is no anal orifice ; in others this orifice exists. 



