445] COLORS OF TIGER BEETLES— SHELFORD 51 



occurs in California where the usual population is green. The physio- 

 logical condition in which no metallic film is secreted is closely related 

 to one in which a metallic film producing green is secreted. 



The secretion of a film which lies at the outside of the primary 

 cuticula in the first work of the hypodermal cells. It would seem 

 that the secretion of such a layer might be inhibited by environic 

 stimuli! at a critical stage in the life of the pupa, but there appears to 

 be no experimental results showing whether or not this is true. If 

 environmental conditions do influence the occurrence of black and green, 

 climatic conditions applicable to all species are not alike (see p. 52). 



In the case of C. scutellaris the green and black forms have least 

 pigment developed in the elytra (black is accompanied by a similar 

 amount), and green in ontogeny is accompanied by least. The amount 

 increases as the reddish color comes in, in lecantei. The amount of 

 pigment in the brilliant red western form is intermediate between the 

 green form and the dark red lecontei. C. splendida, very brilliant, shows 

 much less pigment than limbalis, which is dull. 



Many species, particularly purpurea and pulchra, show more bril- 

 liant colors along the elytra margin where white markings usually 

 occur. This is noticeably true in purpurea, which in the subspecies 

 cimarrona has a complete white margin in many specimens. As a rule 

 when the areas commonly occupied by markings become pigmented the 

 colors in these areas are more brilliant. W. Horn (1915) has called 

 attention to this. As has been noted, the elytral surface of most tiger 

 beetles is made up of small hexagonal pits which jirobably convspond 

 to the hypodermal cells which secreted it (Fig. 1, PI. I). The ridges 

 between these lie over the boundaries of the cells. In the elytra of 

 C. purpurea these pits are smaller in the blue-green margin. The same 

 is true of many other species as shown in Table III. 



Wliile many colors such as green and greenish blue, red, etc., in 

 early ontogeny change to colors of longer wave length during ontogeny 

 and later life, such is not true during ontogeny at least in the case of 

 such purple specimens of C scutellaris. These are rare and only a 

 fe\v specimens from Starved Kock (Utica), Illinois, have been found; 

 .some of these are purplish brown, but one individual was secured in the 

 larval stage and reared (Fig. 558, PI. XXIX). It was purple from 

 the beginning and, never showed any tendency to change, though it 

 was kept for a long time. The same is probably true of the purple 

 forms of C. sexguttata which occur in eastern Kansas; purple forms 

 of nigrocoerulea show no blends with the green. 



tJ? I 



