AMERICAN NEUROPTEKA. llo 



ineutuin, and which have their origin in the floor of the submentuni 

 proximal to the middle hinge, serve to throw the lateral lobe out as 

 the labium is thrust out. The adductors which are inserted at the 

 inner tendenous prolongation of the lateral lobe, and which also 

 originate in the floor of the submentum at a point a little distal to 

 the origin of the abductors, serve to draw the lateral lobe down 

 against the ligula. The extensors have their origin upon the back- 

 ward prolongation of the hypo-pharynx, and passinj^ over the flex- 

 ors and above the adductors near theii' origin, ai'e inserted upon the 

 hind ventral margin of the mentum below the hinge. These exten- 

 sors, by pulling over the basal hinge and the middle hinge, obtain 

 the leverage necessary to throw the entire labium out to its full 

 length. The flexors, originating upon the tentorium, somewhat 

 above the origin of the extensors, and inserting into the supero lat- 

 eral margin of the mentum distal to the hinge, by means of a ten 

 don, fold the labium down into a position of rest. 



Thus by the action of the adductor muscle, in combination with 

 the extensor, the labium is thrust out, the lateral lobes opened, and 

 the moval)le hooks mechanically extended ; then when the victim is 

 within touch, with a movement equally rapid and concerted, the ad- 

 ductor working with the flexor, the lateral lobes are drawn down, the 

 labium closes and the prey is held in a position in wdiich it can most 

 easily be devoured. 



II. ONTOGENY OF THE LABIUM. 



LKNTES. 

 Amazingly various as are the shapes of the labium, more especiallv 

 the shapes of the lateral lobes, in the various families of Odonata, I 

 thought it probable that greater siujplicity of conditions might be 

 discovered in the early nymphal and embryonic stages and that in 

 this way some new light might be tlu'own upon the homologies of 

 parts. With this in view I studied a series of labia of Lestes uncata, 

 beginning with the embryonic stage (PI. V, Fig. 13), the stage at 

 which the development is teni[)()rarily stopped when aestivation 

 begins (see account of the life history of Leste-i by Prof. J. G. 

 Needham in Bull. (i8 of the N. Y. State Museum,' pp. 228-230, 

 1903), and passing through a series of eight nymphal stages up to 

 a condition approximating that of the full gr(twn nymph (PI. 111. 

 Figs. 1-8). 



TRANS. AM. ENT. SOC. XXX. (15) MAY. 1904 



