THE HIDDEN TYPE OF WING-GROWTH 125 



with seven or eight pairs of prolegs, the foremost being on the 

 second abdominal segment. The Scorpion-flies and their 

 allies (Mecoptera) insects sometimes associated with the 

 Neuroptera, but distinguished by their elongate beak-like faces, 

 their predominantly longitudinal wing-nervuration, and the 

 upturned hind abdominal segments of the male with con- 

 spicuous genital armature have as their larvae caterpillars 

 in which the series of prolegs is still more extensive, including 

 possibly nine pairs, which begin on the first abdominal seg- 

 ment ; the prolegs of these larvae show indications of jointing. 

 The caterpillars of saw-flies differ from those of moths and 

 butterflies in having no hooks or spines on the prolegs, which 

 attach themselves to the surfaces on which the larva crawls 

 by a sucker-action, the centre of the disc of the proleg being 

 withdrawn from contact so as to enclose a small airless space. 

 The head of a saw-fly caterpillar has but one simple eye 

 (ocellus) on each side instead of the three or four wherewith 

 the moth larva is provided. In many saw-fly caterpillars the 

 head appears small relatively to the body, when compared 

 with that of a beetle grub or the caterpillar of a moth. A 

 tendency to reduction in the larval head-capsule is indeed a 

 marked feature among insects of the order (Hymenoptera) 

 to which saw-flies belong. Female giant saw-flies (or " wood- 

 wasps," Sir ex) are insects of formidable aspect with the long 

 outstanding ovipositor used for boring timber so as to place 

 their eggs amid food suitable for their larvae. These tree- 

 tunnelling, wood-eating grubs have a soft body with thin, 

 white, flexible cuticle, except that the tail-segment ends in a 

 short, rigid backward-pointing spine. Prolegs are not dis- 

 tinguishable and the thoracic legs are very small, the jointing 

 just defined, but the cuticle feebly chitinized, and the foot 

 segment ending in a soft, blunt tip. The head also is relatively 

 small, its breadth being much less than that of the thorax, 

 so that the larvae offer in this respect a contrast to the soft 

 beetle grubs with legs reduced or wanting described in earlier 

 pages of this chapter (pp. 112-115). The feelers, partly sunk 

 in circular pits, are very small and blunt. The mandibles, 

 adapted for biting wood, are hard and strong ; maxillae and 

 labium have rounded lobes beset with fine spines and very 

 short, relatively thick palps. In the allied family of the stem- 



