DRAGONI^UES AND DAMSEI^I^UES IN PONDI^ISH CULTURE. 239 

 LIBELLULA LUCTUOSA. 



The Egg. — The egg of this species is an almost perfect ellipse, 0,57 mm. long and 0,30 mm. wide. 

 The neck is conical, as wide at the base as it is high, with a distinct basal segment and a divided tip. 

 There is also a short process at the posterior end of the egg; the yolk granules are comparatively large 

 and distinct. Eggs laid on July 12 began to hatch July 22, and the hatching was entirely completed 

 by July 30. Several lots of eggs from this species were hatched during the summer, and the period of 

 incubation was practically the same for each lot. 



The Nymph. — The newly molted nymph is just i mm. in length, exclusive of the antennse; the 

 head and abdomen are the same width, 0.38 mm.; the head is one-fifth wider than long; the hind 

 legs are about the same length as the body, the first two pairs are proportionally shorter; the antennas 

 are a little shorter than the head and rather stout. The head is a deep, sulphur yellow, the eyes are 

 dark orange, with black spots, the digestive canal is light yellow, and the legs are banded with gray and 

 white. 



As soon as the pronymph has molted and becomes a true nymph, the latter swims up to the surface 

 of the water, accomplishing this locomotion by means of the legs, without any help from water ejection 

 at the rectum. Having reached the surface the nymph is able to hold itself there by clinging to the 

 surface film with its claws. It remains there for a long time almost motionless, so that, if the tumbler 

 be examined at any time, the undersurface of the water film will be found covered with nymphs as 



Figs. 38 to 40. — Development of Libellula luctuosa: 38, egg; 39, mask of nevv'ly hatched nymph; 40, newly hatched nymph. 



close together as they can stick. It often happens that one coming up from the bottom finds another 

 already clinging to the film when it reaches the latter. It then fastens to the other nymph instead of 

 to the film, and the combined weight of the two nymphs is more than the film can sustain, so that 

 they sink slowly back to the bottom. Under natural conditions such a seeking of the surface brings 

 the nymphs to the floating algae or other surface vegetation, which is evidently the location they seek 

 for safety and food. It is also possible that the young nymph, like the teneral imago, needs the stronger 

 sunlight for hardening its chitin integument and maturing its color pattern. 



The Mask. — Mentum twice as wide as long; distal margin two times the length of the proximal; 

 four setae on the inner surface along either side near the lateral margin; three mental setse on each 

 side of the center in a straight line; a toothed prominence on the midline behind the distal margin. 

 Lateral lobes one-half longer than wide ; two marginal setae on the outer border near the base ; two lami- 

 nate setae on the blade of the lobe near the inner margin; raptorial seta just reaching the tip of the 

 movable hook, the latter long and slender; distal border of lobe with five teeth near the outer corner, 

 the second tooth the longest. 



