146 



ORGANIC EVOLUTION 



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whose larvae are parasitic upon other insects, closely 

 resemble the form upon which their larvae are parasitic, 

 being enabled thus to escape detection when approaching 

 to lay their eggs in the nests of the species whose members 

 will become infested with their larvae. These parasites 

 live chiefly upon different kinds of bees. 



Signals and recognition marks. 



Signals and recognition marks are seen in many animals. 

 Birds and mammals especially display these. Our com- 

 mon rabbit, when startled, 

 lifts his tail as he runs, 

 the white on the under 

 surface and on the flanks 

 under the tail showing 

 almost like a flash of 

 white light. This brill- 

 iant white patch is sup- 

 posed to serve as a signal 

 to other rabbits, especially 

 the young, to seek in 

 flight safety from some 

 impending danger (Fig. 43). Our common eastern deer 

 have a similar white spot on the under surface and below 

 the tail, which serves the same purpose. Some of the 

 western American antelopes have upon the flanks a much 

 larger patch of long white hairs, which when expanded by the 

 contraction of the skin muscles and the consequent erec- 

 tion of the hairs, flashes out as a white signal visible on 

 the plains for miles (Plate 81). Similar white rump patches 

 are found in some of the African gazelles. 



FIG. 43. Common "cottontail" rabbit, which is 

 startled and about to run. The tail is lifted enough 

 to show a part of its white under surface and the white 

 rump patch. From a photograph from life by E. R. 

 Warren. 



