AMERICAN NEUKOPTERA. 115 



After the tburtli moult (PI. Ill, Fig. 4) a differentiation is notice- 

 aljle among the end teeth, the two at the extreme edges becoming 

 slightly larger than the others and turning outward, away from 

 them. Two setae make their appearance on the mentum. In the 

 next stage (PI. Ill, Fig. 5j the principal change is in the gradual 

 disappearance of the sutural line, the rest of the deveh)pment seems 

 to be practically stationary. 



In the sixth of the series (PI. Ill, Fig. 6) a second seta makes its 

 appearance upon the movalile hook, while the terminal teeth of the 

 end group have become larger and are separated from the others l)y 

 deeper clefts. Three setse appear upon the mentum on either side. 

 In the succeeding stage (PI. Ill, Fig. 7) the separation between the 

 terminal teeth of the end group and their companions has increased 

 and there is an increase in the number of teeth on the border of the 

 ligula. In the stage represented in Plate III, Fig. 8, we find a con- 

 dition very similar to that of the full grown nymphal labium. A 

 third seta has developed on the movable hook and three are present 

 on the mentum. The clefts between the end hook and the end teeth 

 and the terminal teeth of the end group and the central ones have 

 reached, their maximum depth. The number of teeth on the inner 

 edge of the lateral lobe and on the ligula has reached its maximum. 

 The line beneath the border of the ligula has become a mere trace, 

 the tooth which figured so prominently in the early stages being 

 represented by a chitinized spot. The cleft in the ligula has reached 

 its greatest depth. With the exception of a few additional seta" 

 upon the mentum, this stage represents the full-grown nymphal 

 labium ; no more changes take place until the transformation from 

 nymph to adult. 



ANAX and BASI/ESCH»r A. 



The t^er'ies of Anax Jni) ills contains two nymphal labia in differ- 

 ent stages of development, and two embryonic labia. In the young- 

 est end)ryonic labium (Plate IV, Fig. 1) the mentum is composed 

 of two lobes separated by a deep cleft running almost to the sub- 

 mentum. The ligula is as yet undeveloped. The movable hook is 

 not as yet separated from the rest of the lateral lobe; in shape it 

 strongly resembles the palpus of the maxilla. In the succeeding 

 stage (PI. IV, Fig. 2) we have a condition much further advanced 

 and comparable to the embryonic labium of Lestes uncain (PI. V, 



TKANS. AM. ENT. SOC. XXX. MAY. 1904 



