HEMIPTERA. 137 



young are afterward hatched, or in place of these 

 pseudova, the young may be enveloped at birth only 

 by a thin pellicle, which they immediately burst. 



Many broods are produced during the warm weather. 

 The last brood is brought forth at the approach of 

 cold weather, and differs from the preceding in being 

 largely made up of perfect males and females.^ Some 

 of the agamic individuals may survive through the win- 

 ter and reappear in the spring. 



It has been proved by experimentation that Aphides 

 can be kept in a room maintained at a proper heat for 

 four years, and in the case of the two species tried, 

 no sexually perfect males and females were hatched. 

 The failure of proper nourishment, even in warm 

 weather, may be the cause of the premature produc- 

 tion of a sexually perfect generation. Thus the per- 

 petuation of the species is secured not only by the 

 winged agamic members of the community, but, in the 

 event of a failure of food through any cause, drought, 

 etc., even in warm weather, or in case of danger aris- 

 ing from the approach of cold weather, still further 

 security is provided in the generation of sexually per- 

 fect males and females, the latter of which produce 

 true ova. The Aphides can be easily kept in the 

 schoolroom and studied. They are found on neg- 

 lected house-plants, and are often crowded together in 

 great numbers upon the leaves and stems. Their hab- 

 its and characteristics are not difficult to observe, and 

 a little care and patience will produce results which 

 will amply repay both teachers and pupils. 



1 For drawings illustrating the development of Aphis, see 

 Huxley, Trans. Linn. Soc, London, Vol. XiiCII.; also Corn- 

 Stock, Introd. to Etttomology, p. 155. 



