310 JAMES W. McCOLLOCH AND H. YUASA 



the plants were kept in the liquid while the remainder of the 

 plant was outside the bottle. The plants were held in place 

 with a cotton stopper in the mouth of the bottle. This method 

 proved very satisfactory because of the fact that the plants 

 could be handled conveniently and the various stages of the fly 

 could be studied with greater ease and exactness than when 

 the plants were grown in soil. 



OBSERVATIONS 



Eggs. — The egg of the Hessian fly is very minute, being only 

 about 0.5 mm. in length, cylindrical, obtusely rounded at the 

 ends, glossy, translucent and pale yellowish red. This color 

 deepens with the development so that just before hatching it 

 is distinctly reddish in color. About the second day after 

 deposition the posterior end of the egg becomes opaque, and 

 shows no reddish content. This is very characteristic of the 

 fertilized egg. The caudal extremity of the embryo is located 

 in this end of the egg. Generally, the eggs are laid on the 

 upper surface of the leaf, being glued into the longitudinal creases 

 of the leaf -blade. Frequently the eggs are laid on the lower 

 side of the blades of wheat plants, and occasionally on the stalk. 



Hatching of Eggs. — The majority of eggs hatched in about 

 60 to 72 hours after deposition under the experimental condi- 

 tions of the breeding chamber where the mean temperature was 

 70° F. and the mean relative humidity 70%. The exact method 

 whereby the hatching occurs is not as yet ascertained. The 

 egg-shell seems to split along its cephalo-dorsal aspect and the 

 larva emerges quickly. Enock (1891, p. 333) records some 

 observations on the hatching of the eggs. He found that the 

 movements of the inclosed larvae could . be distinctly seen on 

 the third day and on the fourth day he was able to distinguish 

 the muscular efforts of the larvae to burst open the shell, which 

 they succeeded in doing after three or four hours work. 



Orientation of the Larva. — Immediately after emerging from 

 the shell, often before the body is more than one-half out of 

 the egg-shell, the larva begins to turn sidewise, describing an 

 arc and finally orients itself in the direction exactly opposite 

 to that in which it had been within the egg (Fig. 1). This 

 orientation behavior was first noticed when larvae, hatching 

 from the eggs laid by a female held in an inverted position on 



