Vol. xxiii] ENTOMOLOGICAL NEWS I5I 



birth. Professor Woodworth, in the paper quoted above, 

 has pointed out that a distinction may be made between the 

 two forms as soon as they have accompHshed their first molt, 

 thus placing one limit to this critical period. These experi- 

 ments were conducted in the following manner : A cutting 

 of rose bearing a number of young apterous viviparous ap- 

 hids {Nectar ophora rosae) was planted in a four-ounce 

 tumbler containing washed and sterilized sand and watered 

 v/ith a saturated solution of magnesium sulphate. In a like 

 manner a cutting with aphids was wetted with water. Since 

 in the former experiments the aphids born during the first 

 three days did not show the effect of the salt, three days were 

 permitted to pass and then as soon as the young were born 

 on the plant treated with magnesium sulphate they were 

 carefully transferred to a fresh cutting bearing no aphids 

 planted in sand, to which only pure water had been added. 

 Those born on the plant in water were likewise transferred 

 just after birth to a plant bearing no aphids, which had been 

 planted in sand watered with magnesium sulphate. The fol- 

 lowing table shows the results : 



Chemicals used 



Plant on which birth occurred MgSO^ H ^O 



Plant to which newly born aphid was transferred ..HgO MgSOi 

 Per cent, developing wing pads o 100% 



From this table it will be seen that the efifects of mag- 

 nesium salts on the wing production of aphids is due strictly 

 to the salt taken by the insect after birth and that the feeding 

 during the first day of its existence determined its future de- 

 velopment. 



These experiments do not answer the question whether the 

 magnesium is a stimulant to the development of wing-buds 

 or a retarder of the general development, but the much slow- 

 er development of the ovaries and the slower increase in to- 

 tal body weight, which has been readily observed in the ex- 

 periments, would seem to favor the latter idea. 



The writer proposes to show the morphological diflFeren- 

 tiation between these two forms which occur during this 

 stage in a subsequent paper. 



