Practical Considerations. 151 



similar to those above given ; and all point to the conclu- 

 sion that where the newly-hatched insect has not the 

 natural channel of exit (described on p. 72) which was pre- 

 pared by the mother, it must inevitably perish if the soil 

 be moderately compact, unless cracks, fissures, or other 

 channels reaching to the surface are at hand. 



From the above four series of experiments, I would 

 draw the following deductions, which have important 

 practical bearing : 



First — Frost has no injurious effect on the eggs ; its 

 influence is beneficial rather, in weakening the outer shell. 



Second — Alternate freezing and thawing is far less inju- 

 rious to them than we have hitherto supposed, and tends 

 to their destruction, if at all, indirectly, by exposing them 

 to the free air. 



Third — The breaking open of the egg-masses, and ex- 

 posure of the eggs to the atmosphere, is the most effectual 

 way of destroying them. Hence the importance of har- 

 rowing in the fall is obvious. 



Fourth — Moisture has altogether less effect on the vital- 

 ity of the eggs than has heretofore been supposed, and 

 will be of little use as a destructive agent, except where 

 land can be overflowed for two or three days at the time 

 when the bulk of the young are hatching. 



Fifth — Plowing under of the eggs will be effectual in 

 destroying them, just in proportion as the ground is after- 

 ward harrowed and rolled. Its effects will also necessarily 

 vary with the nature of the soil. Other things being equal, 

 fall plowing will have the advantage over spring plowing, 

 not only in retarding the hatching period, but in permit- 

 ting the settling and compacting of the soil ; while where 

 the ground is afterwards harrowed and rolled, the spring 

 plowing will prove just as good, and on light soils perhaps 

 better. 



