entiated free-living organism (larva), which is The success of the Insecta as a class (nearly extensively destroyed and rebuilt into a mor­ 1 million spp.; phylum Arthropoda) is largely phologically different form (adult) suitable for due to their adaptability to profoundly different ecological niches. Insects have attracted the life in a different ecological niche, is controlled attention of scientists both as useful model by a single genome. This is probably the most systems for the study of many basic biological dramatic reorganization of a growing animal phenomena, and also for the rational develop­ known. Certain carefully selected insect ment of new methods of controlling the pest material can, thus, provide suitable model species. As a class, insects have played an systems for developmental studies. important role in the elucidation of numerous The majority of the individual metabolic basic biochemical phenomena. For example, reactions occurring in insects are similar to work on the genetic control of eye pigment those found in other groups of organisms.