326 PERIPATUS, MYRIOPODS, AND INSECTS. 



other hand, our indebtedness to hive bee and silk moth, to 

 cochineal and lac insects, to those which destroy injurious 

 insects, and to those which carry pollen from flower to 

 flower, is obvious. 



Finally, we must at least mention that in ants, bees, 

 wasps, and termites we find illustration of various grades of 

 social life, and marvellous exhibitions of instinctive skill as 

 well as some intelligence. 



Pedigree. 



Insects must have appeared relatively early, for remains 

 of a cockroach-like form have been found even in Silurian 

 strata. The higher forms with complete metamorphosis 

 appear much later (e.g., beetles in the Carboniferous ages), 

 but it seems that the Palaeozoic Insects were mostly 

 generalised types, prophetic of, rather than referable to, the 

 modern orders. 



As to the pedigree of Insects, the wingless Collembola 

 and Thysanura are doubtless primitive. They lead us back 

 to some of the less specialised Myriopods (e.g., Scolopen- 

 drella\ back further to Peripatus, which helps to link the 

 Tracheate to the Annelid series. 



But though the primitive wingless insects, the simple types 

 of Myriopods, and Peripatus represent ascending steps in 

 evolution, what the actual path has been we do not know. 



