ARTHROPODA 



299 



fields of vegetation. Since the settlement of the regions where they breed, with 

 the ploughing up of the eggs and the destruction of the young, there is reason to 

 hope that these migrations are at an end. Accounts of similar migrations of 

 locusts are recorded in the history of the old world. These migrations and their 

 effects illustrate how climatic conditions in one locality may change the balance 

 of life in another. The second chapter of the prophet Joel gives a vivid account 

 of a visitation of locusts. See Fig. 139. y 



Fig. 138. 



Fig. 13S. Camiiodea, — a Thysanuran. Magnilied 30 times. By J. W. Folsom. 



Questions on the figure. — In what respects does this form seem intermediate 

 between the Myriapods and the higher insects? How does this compare with the 

 larvae of insects which undergo a metamorphosis? Can you distinguish head, 

 thorax, and abdomen? 



Other Orders. — Some of the smaller orders are as follows: the Ephemerida, or 

 May flies whose adults may live for only a few hours, although the larvae may 

 require from one to three years to develop; the Odonata, or carnivorous dragon- 

 flies, and damsel-flies; the Plecoptera, or stone-flies; the Isopiera, or termites (white 

 ants) which are social, polymorphic forms; the Corrodentia, book-lice and bark- 

 lice; the Mallophaga, parasitic bird-lice which eat hair and feathers; the Thysan- 



