134 



SCIENCE 



[N. S. Vol. LIV. No. 1389 



portant to remember that after the revolution 

 of the embryo the eggs are much more suscep- 

 tible to contact and similar ipjury. Recently 

 Peterson^ has published an important paper 

 on the hatching of the eggs of these species, 

 but he has apparently failed to note the fact 

 that the time of revolution is extremely im- 

 portant in interpreting the results of experi- 

 ments. It is very probable that the revolution 

 of the embryo in New Brunswick takes place 

 considerably later than in Washington. 

 Judging from the conditions this would in all 

 probability begin during the first week in 

 April. It is evident then that in eggs taken 

 during most of March and possibly some of 

 those taken early in April the embryos would 

 still be in the resting s*age. Under such con- 

 ditions eggs placed under a high temperature 

 for hatching purposes would fail to hatch as 

 all the embryos would be killed. In exami- 

 ning Peterson's Table I., p. 16, it will be seen 

 that out of 4,400 eggs of pomi taken on March 

 14, not an egg hatched at 80° F., whether in 

 dry air or in different i)ercentages of satura- 

 tion. Other eggs taken on April 6, gave a 

 variable percentage of hatch. In dry air 

 (ezpt. 105) some hatching occurred and also 

 in 63 per cent, and 100 per cent, of moisture, 

 but in 22 per cent, moisture (expt. 106) no 

 hatching occurred. It seems probable that 

 many of the embryos in the eggs used had not 

 revolved and that more such eggs were present 

 in experiment 106 than in erperiments 105, 

 107 and 108. In fact these results seem to 

 eontradict Peterson's conclusion for more 

 hatched in dry air than in 22 per cent, 

 moisture in which there was no hatch what- 

 ever. Certainly since more hatched in dry 

 air than in 22 per cent, moisture one can not 

 claim that it was lack of moisture which pre- 

 vented the hatch. Some other factor must 

 have been at work and this factor was evi- 

 dently the condition of the emb^ryo. 



The writer does not intend to convey the 

 impression that moisture has no influence on 

 the hatching of these eggs for, as Peterson in- 

 dicates, it undoubtedly has but he wishes to 

 point out the fact that in experiments of this 



a New Jersey Agr. Exp. Sta. Bull. No. 332, 1919. 



kind the stage of embryonic development must 

 be considered if accurate conclusions are to be 

 drawn. 



Thus the small percentage of hatch secured 

 by Gillette in Colorado is explained by Peter- 

 son entirely on moisture conditions and yet 

 the writer has just shown that the failure 

 to hatch in some of Peterson's own experi- 

 ments with pomi is due to an entirely differ- 

 ent factor. 



The hatching of the different species takes 

 place in very much the same way although 

 prunifoliw is much earlier than pomi and 

 malifolim which two hatch at approximately 

 the same date. 



After revolution of the embryo hatching 

 can be advanced or retarded greatly by 

 weather conditions. An elevated temperature 

 which before this time is fatal serves after- 

 wards to hasten hatching unless the at- 

 mosphere is extremely dry. The gelatinous 

 matrix in which the egg is embedded has by 

 this time become more or less brittle and 

 splits irregularly, usually in a longitudinal 

 direction. This is soon followed by a rupture 

 in the shell made by the egg burster. The 

 young nsTnph continues to push its way out- 

 ward until it stands in an erect position just 

 above the slit in the shell. At this time the 

 membrane has not ruptured and the aphid 

 sometimes dies without freeing itself. Nor- 

 mally, however, the membrane ruptures to the 

 right of the egg burster and gradually works 

 downward carrying this structure with it. The 

 young insect then leaves the egg and this thin 

 pellicle is left as a shrivelled structure partly 

 protruding from the slit in the shell. In 

 speaking of the fate of tlie egg burster Peter- 

 son (J. c, p. 14) says: "During emergence 

 this ridge disappears and only a faint line 

 remains along the meson." As far as our ob- 

 servations go, however, the egg burster retains 

 its identity as part of the membrane in much 

 the same way as that of Gorydalus cornutus, 

 described by Riley. In some cases the writer 

 has observed young of viviparous aphids to 

 free themselves while on the leaf. Packard* 



3 ' ' Text Book of Entomology, ' ' 1909, The Mae- 

 millan Co., p. 583. 



