MOLTING. 61 



present. The size varies greatly in nearly all forms, wingless viviparous females 

 varying from 1.5 mm. to over 2 mm. 



Measurements of antennal joints (average for 8 specimens): I, 0.069 mm.; II, 

 0.045 mm.; Ill, 0.210 mm.; IV, 0.135 mm.; V., 0.140' mm.; VI, base, 0.089 mm. 

 VI, filament, 0.305 mm.; total length, 0.993 mm. 



Pupx (fig. 14). — Measurements of antennal joints (average from 8 specimens): 

 I, 0.064 mm.; II, 0.056 mm.; Ill, 0.186 mm.; IV, 0.127 mm.; V, 0.134 mm.; VI, 

 base, 0.090 mm.; VI, filament, 0.270 mm.; total length, 0.927 mm. 



Winged viviparous female (fig. 7). — Measurements of antennal joints (average from 

 8 specimens): I, 0.082 mm.; II, 0.059 mm.; Ill, 0.300 mm.; IV, 0.223 mm.; V, 

 0.215 mm.; VI, base, 0.110 mm.; VI, filament, 0.395 mm.; total length, 1.384 mm. 



MOLTING. 



The time required for molting, from beginning to completion, is 

 30 minutes. The first indication is restlessness; the antennae are 

 waved continuously and the legs move jerkily. This period of 

 restlessness continues for 10 minutes, after which the antennae are 

 allowed to come to rest close down upon the dorsum. A few minutes 

 later the tip of the abdomen will appear transparent and baggy, due 

 to the old skin having slipped backward; the head and eyes are now 

 being freed. It appears that the skin first ruptures in the cephalic 

 region and only splits a part of the length of the dorsum, the insect 

 gradually working its way out from this extremity. After the head, 

 the antennae are the first to be liberated, then each pair of legs in 

 succession, and after all of the appendages have been freed the insect 

 has still to struggle somewhat to free its abdomen. These observa- 

 tions were made on individuals casting the third or fourth molt. 



NUMBER OF MOLTS. 



Quite a number of observations were made on the number of molts 

 and the period between the same, ft being learned that stem mothers, 

 the summer forms, and the sexes molt 4 times only. 



To facilitate caref id and accurate observations upon the number of 

 molts, a young wheat plant was potted in a 5-inch flowerpot. A 

 circle of black paper was cut small enough to fit down in the top of 

 the pot. A small hole was then cut in the center and the paper disk 

 was then fitted closely down about the base of the plant. After the 

 paper was in nlace the space immediately around the plant was filled 

 in with absoroent cotton made black with waterproof ink. Then a 

 young Toxoptera that had just been born was placed on the plant 

 inclosed by a clean lantern globe, with a piece of new cheesecloth 

 firmly secured over the top to prevent the grajush cast skins from 

 being overlooked. Each cast skin was removed as soon as the molt 

 was completed, and a record made so that it could not possibly be 

 counted a second time. All observations recorded in the notes on 

 molting were made in this manner. 



