230 THE UNIVERSITY SCIENCE BULLETIN. 



at its base and the loose ends peel back, one of them bearing the at- 

 tached micropyle. The process is now best viewed from the side. First 

 a clear bubble appears, bound by a delicate transparent membrane. 

 This grows until it reaches a height about one-fifth that of the egg, and 

 stops. Then gradually the head of the nymph comes up and fills the 

 bubble. (See pi. XXVIII, fig. 12.) The process so far may have consumed 

 some three or more minutes, but the nymph is not yet free. Another 

 heave, the membrane that enclosed the bubble splits and a moment later 

 the nymph, plastic and soft like a worm, swells the exposed part of the 

 body repeatedly until it is all but free. Then it may lie exhausted a 

 few moments, or even minutes, before a final kick sets it at liberty. 

 As soon as it is liberated it is capable of swimming rapidly for several 

 centimeters, and then appears exhausted. It begins feeding before the 

 color pattern is complete. 



The hatching process takes place under the water, and the behavior 

 of the new-fledged nymph in relation to an air supply is noted below. 

 The time required for emergence from the egg ranges from four or five 

 minutes to a half hour. One egg began hatching at 3.51 p.m. The 

 parts of the shell peeled back in six divisions. Midway between the 

 eyes at the apex of the hatching nymph there was an organ that pul- 

 sated vigorously at times. At 4:15 the upper edges of the red eyes • 

 began to show and the part before the eyes was larger than the re- 

 mainder of the head. One-half of the eyes was exposed at 4:25. Body 

 completely out at 4:31. The limbs of the nymph, incased in the shell, 

 are stretched caudad upon the venter, and the margins of the body are 

 rolled ventrad. The ventral side of the nymph is on the bulging side 

 of the egg, and there is a deep transverse fold on the dorsum, so that 

 the back of the head and dorsal abdominal glands are approximate. 

 Figures of the hatching nymph are shown on pi. XXVIII, fig. 12. The 

 remains of this thin embr^ onic sheath lie about the opening of the 

 abandoned egg like a cast-off garment. (See fig. 12.) 



Behavior of Newly Hatched Nyynphs. The nymph just freed from the 

 egg shell presents little pigmentation. The limbs and the flat margin 

 of the entire body are as transparent as glass. The head and central 

 part of the body is pale yellow. The eyes are red and the two dorsal 

 abdominal glands are a pale red. There are two faintly pale pink in- 

 definite regions laterad of the middle line on the thorax. 



This transparency makes it possible to study the question of respira- 

 tion, for as soon as the tracheae fill with air they become silvery. There 

 is still a large problem to solve relative to the reception of the first air 

 supply. Tillyard's work with the dragon-fly nymphs suggests an inter- 

 esting field of study with Corixid nymphs. A few observations were at- 

 tempted in a preliminary way. Eggs ready to hatch were placed in a 

 slide cell, the chamber filled with water and covered over with a glass 

 cover slip. The only air then available to the nymph would be such as is 

 found dissolved in water. By the time the nymph was a half hour old, 

 however, there usually collected a bubble of gas somewhere under the 

 slip. In those nymphs observed the tracheae remained undefined until the 

 little bug made contact with one of these bubbles, whereupon they im- 



