104 INSECT TRANSFORMATION 



on the inner surface as well as a slender movably articulated 

 tooth or spine (prostheca) ; at the base of the inner aspect is an 

 extensive molar or grinding area. The maxilla (Fig. 56, d) 

 conforms with remarkable closeness to the type found in adult 

 biting insects ; there is a stout, horizontal cardo (c) to which is 

 jointed the broad, spiny stipes (s) bearing a narrow bifid lacinia 

 (I), a sharply pointed galea (g), and a three-segmented palp (p). 

 In the ground-beetle larva it will be remembered that the 

 maxilla is much simplified as compared with that of the adult ; 

 this condition is found among beetle larvae generally, so that 

 the very slight divergence of the dascillid larva from the imago 

 in this respect is especially noteworthy. The labium (Fig. 

 56, e) of this larva with its two-segmented palps does not differ 

 markedly from that of the ground-beetle grub, except that the 

 ligula is broadly lobate instead of narrow ; the interest of the 

 labium in the Dascillus larva is that its basal regions (mentum 

 and sub-mentum) are clearly continuous with the cuticle of the 

 neck-region, as they are in a grasshopper or a cockroach (see 

 p. ii above). The ventral sclerite of the true head-capsule 

 lies distinctly in front of the labium, so that the latter appears 

 to belong, without doubt, to a segment situated behind the 

 original head ; reasons have already been given (p. 12) for 

 regarding this character as primitive. And a further primitive 

 feature is shown by the Dascillus larva, for when the tongue 

 (Fig. 57), a flexible chitinous plate supported by strong ridges 

 produced backwards into " feet ", is examined, a pair of pro- 

 minent, rounded, toothed lobes (Fig. 57 A) are seen on its front 

 surface ; these are maxillulae the pair of small appendages, 

 behind the mandibles, whose presence as already explained 

 (pp. 11-12) indicates the primitive standing of those insects in 

 which they are found. In the Dascillus larva the maxillular 

 teeth appear to be of service in mastication, as they lie imme- 

 diately below rows of denticles within the labrum or upper lip. 

 To the same family as Dascillus belong a number of small 

 beetles which live for the most part, submerged in the water of 

 streams and ponds. These (Helodes and Hydrocyphon for 

 example) have larvae of a curiously flattened form adapted for 

 crawling on the under surface of stones or between the broad 

 leaves of aquatic plants, the flattening being due to a strong 

 development of the lateral regions (pleura) of the cuticle of 



