104 MOSQUITOES OF NORTH AMERICA 



" The pupa begins to straighten the abdominal part while in the meantime 

 the cephalothorax retains its position. The straightening does not occur sud- 

 denly or by jerks, but steadily. After 10-15 minutes the operation is concluded. 

 Already before this the excretion of air between the epidermis (of the imago) 

 and the pupal skin has begun ; the pupa then appears silver-white. Finally the 

 anterior parts of the cephalothorax are raised by a powerful jerk and now the 

 pupa touches the water-surface, in front with the dorsal parts of the pro- and 

 mesothorax, in the middle with the stigmata of the breathing tubes, and behind 

 with the end of the body. The previously strongly convex dorsal surface of the 

 animal has become concave. 



" Now the pupal skin breaks exactly along the median line on that part of the 

 cephalothorax touching the water-surface, and at once there issues into the air, 

 through the gaping slit, the scale-covered, dry dorsum of the imago. By jerks 

 the slit is widened ; soon two transverse slits are added on each side, and after 

 the pupal skin has receded about ten times (synchronous on the two sides) the 

 thorax in its entire width appears in the cleft. Now the scutellum, the stretched 

 neck and the vertex of the strongly downward bent head also appear. The push- 

 ing forward of the mosquito's body by jerks then ceases and the animal issues 

 from its prison, like the actor from a trap-door, with truly ghost-like steadiness 

 of motion. 



" When the head is born the antennae, which lie in special chitinous sheaths 

 on the sides of the cephalothorax, first become free ; then the palpi and proboscis, 

 which are enclosed in a tapering sheath lying loosely upon the pupal case, are 

 disengaged. 



" The abdomen in the meantime has of course also moved further forward 

 and the last segments of the pupal skin are inflated with air. 



" The insect now raises the head and extends the antennae, palpi and pro- 

 boscis ; then it draws the anterior pair of legs from their sheaths by bending the 

 knee-joints, and later also the joints of the feet, in a plane with the body-axis. 

 After the front legs are freed the middle legs are extracted in the same manner 

 and now both anterior pairs of legs are extended forward and outward as far as 

 possible and the tarsal joints are placed gently upon the water. Now the mos- 

 quito's body, which had heretofore only balanced on the air-filled pupal skin, is 

 supported at five points and its equilibrium has become very steady. Then 

 finally the hind legs follow. 



" All the legs are disengaged independently of the movement of the body 

 itself. They are extracted from their sheaths in pairs, by repeated very short 

 movements. 



" Finally the wing tips and the end of the abdomen become free. 



" The entire process is completed within a few minutes. 



" The complete insect issues from the floating pupal skin almost colorless, 

 translucent and strongly inflated and assumes its permanent color and form 

 after some hours. 



" The study of the motive power in the process of ecdysis gives highly in- 

 teresting results. 



" In the first place, as already remarked above, the pupal skin, which had be- 

 fore been in close contact with the mosquito's body, is detached and inflated to 

 the utmost by a layer of air which is pressed out of the stigmata of the imago. 

 The previously dark pupa becomes shining silvery. The increasing pressure 

 within causes the pupal skin to burst at its weakest point over the thorax and at 

 the same time tears the connection of the breathing trumpets with the tracheal 

 system of the mosquito. 



" Now the layer of air surrounding the mosquito's body stands in direct con- 

 nection with the atmosphere and at once the animal begins to swallow great 

 quantities of air. 



