210 A BOOK OF INSECTS 



migrate to the stems of corn or grass, on which plants 

 another cycle of generations is produced. In the genus 

 Chermes, which frequents conifers, very complicated life- 

 cycles appear to be the rule. The successive generations 

 of the species known as Chermes abietis have been in- 

 vestigated by Continental observers, and may be briefly 

 tabulated as follows : — 



First. A wingless, parthenogenetic female hibernates 

 on the spruce or Christmas tree, and in the spring lays 

 numerous eggs at the tip of a young shoot, thus giving 

 rise to the familiar pine-apple gall, or false cone. 



Second. The young that hatch from these eggs 

 develop in the cavities of the gall, and after their final 

 moult become winged females — a few of which remain 

 on the spruce, where they lay their eggs. From these eggs 

 are produced young that grow into wingless, hibernating 

 females, which next year produce galls exactly as their 

 grandmothers did. But many individuals of this (the 

 second) generation migrate to the larch tree, where they 

 lay their eggs on the leaves or " needles." 



Third. These eggs give rise to a third generation of 

 wingless, parthenogenetic females which resemble their 

 grandmother — i.e. the foundress of the series. They hiber- 

 nate on the trunk of the tree, and protect themselves by 

 a waxy secretion which, from a distance, has the appear- 

 ance of frozen sleet. In the spring they lay their eggs 

 upon their " intermediate conifer," the larch, but no gall 

 is formed. 



Fourth. These eggs give rise to the fourth genera- 

 tion, which is dimorphic, being composed of (1) wingless 

 individuals like the parent form, thus resembling their 

 great-grandmother, and (2) winged forms resembling those 

 of the second generation. The former lay their eggs on 

 the larch, and thus give rise to a wingless stock which 



