432 



GENERAL BIOLOGY 



cance, where only structural and physiological colors are 

 present. Such furnished the materials out of which adapta- 

 tion could proceed by natural selection. Feathers, for 

 example, were structurally adaptable to longitudinal streak- 

 ing, and birds have furnished most of those streaked patterns 

 among animals that fit into a grassy environment. The 

 family Syrphidae of Diptera, which has furnished our most 

 numerous examples of mimicry of the stinging hymenop- 

 tera was doubtless predisposed toward the colors and forms 

 of that family from the beginning ; likewise the crane flies 

 that imitate grass spiders. Doubtless the discerning powers 

 of the predatory species have improved with the disguises 

 of their prey. It would be too much to expect in the nature 

 of the case that the devices always work, and when we 

 examine a series of any adaptive forms, we find such varying 

 degrees of excellence as indicate that the fitting process 

 is still in progress. 



Study 59. Examples from the local fauna of the principal 

 types of animal coloration. 



Apparatus needed. Individual insect nets and cyanide 

 bottles, note books and pencils; if coloration of birds is to 

 be specially observed, opera glasses will be of assistance. 



The most abundant supply of material will be obtained 

 by "sweeping" the grass with the insect net, for protectively 

 colored forms and collecting from flowers for the other two 

 groups. Hand picking from the trunks of trees, etc., will 

 also be useful. 



The record. It is essential that the record called for 

 below be made in the field, each species being studied in its 

 proper habitat, where alone the significance of its coloration 

 can be seen. 



Include in the tables a few well selected examples and 

 omit doubtful cases. 



