August 12, 1921] 



SCIENCE 



135 



tas reported the casting of the amnion of 

 Melanopus spretus while the nymph is free 

 from the egg and mentions observing this con- 

 dition in the hatching of several other insects. 

 In fact, it has been observed that very many 

 insects, including the seventeen year cicada, 

 are entirely enclosed in this membrane after 

 hatching. 



In the aphids as the embryo revolves the 

 serosa contracts and draws with it the cells of 

 the polar organ and the serosa and polar organ 

 from the dorsal plate. This then invaginates, 

 forming the dorsal body which separates itself 

 from the amnion completely and is ultimately 

 absorbed. Thus only the serosa and polar 

 organ disappear while the amnion closes the 

 gap and remains as a distinct membrane over 

 the embryo. This membrane separates, re- 

 mains distinct, and, as previously indicated, 

 is left behind as a thin, transparent membrane 

 by the hatching nymph. 



Headlee* has stated that " A third layer may 

 be seen as the nymph hatches, but this is 

 probably the first-cast skin of the nymph," 

 and this view seems to be held also by Peter- 

 son (I. c, p. 10) who says, " This layer is shed 

 by the nymph as it emerges, consequently it 

 must be an exuvium." The writer is unable 

 to agree with this view for the exuvia cast 

 by the nymph during its growth are quite 

 different from this embryonic membrane 

 which it leaves behind when hatching. 



After the embryo has revolved and is pro- 

 ceeding toward hatching the egg is in much 

 more critical condition than during the dor- 

 mant period. It is less protected by reason of 

 the fracture of the gelatinous matrix en- 

 closing it and the embryo which is actively 

 growing is more susceptible to the effect of 

 spray solutions. This undoubtedly explains 

 the varying results obtained by different work- 

 ers in spraying experiments on aphid eggs. 

 In many lots wherein the embryo had revolved 

 good results were obtained, whereas in other 

 lots where no revolution had taken place, 

 hatching was about normal. In this connec- 

 tion it is important to bear in mind that pomi 



* New Jersey Agr. Exp. Sta. Bull. No. 328, 1918. 



and malifoliw revolve at about the same 

 period, the middle of March in "Washington, 

 and that early in April these eggs are very 

 susceptible to treatment with such sprays as 

 lime sulphur. At the time these eggs are in 

 this critical period of embryonic development 

 those of prunifoliw have hatched and the 

 young are in the first or rarely the second 

 instar. These young nymphs are not affected 

 greatly by lime sulphur but are easily killed 

 by nicotine sprays. 



It seems clear therefore, than in intrv- 

 preting hatching records of aphid eggs in the 

 course of spraying or other experiments, ac- 

 count must be taken of the condition of the 

 embryo in regard to revolution. Knowledge 

 of this fact is also essential in practical 

 control work. Thus in the case of the three 

 apple aphids here considered, the recommenda- 

 tions for use of the combined lime-sulphur- 

 nieotine spray as a " delayed dormant " treat- 

 ment, is seen to be based on scientific reasons 

 — the lime sulphur to destroy the later hatch- 

 ing eggs, principally pomi and malifoliw, and 

 the nicotine for the already hatched aphids. 

 A. C. Baker 



U. S. Bureau op Entomology, 

 Washington, D. C. 



THE AMERICAN CHEMICAL SOCIETY 



{Continued) 



SECTION OF CELLULOSE CHEMISTRY 



Harold Hibbert, chairman. 

 G. J. Esselen, Jr., secretary. 



Effect of adding various cliemioals to wood 

 previoiis to distillation: L. E. Hawley. Several 

 different chemicals have been mixed with wood 

 and the mixture distilled for the determination of 

 the effect of the chemical on the yield of valuable 

 products. The chemical was mixed with the saw- 

 dust by sprinkling in case it was water soluble 

 or by mixing the solid in ease it was insoluble. 

 The mixture was then briquetted and the briquets 

 distilled in a special retort in which mechanical 

 pressure could be applied to the briquets during 

 distillation. The only chemical tried which had a 

 beneficial effect when used in reasonable quanti- 

 ties was sodium carbonate. When about one per 

 cent, of sodium carbonate is mixed with wood 

 previous to distillation the yield of methyl alcohol 



