100 



KINETIC HORMONES — I 



pallor (index 1.5, Figs. 3-14 and 3-20). In darkness the melano- 

 phores assume an intermediate condition (index 2.7). These 

 reactions are similar to those of the red pigment of Palaemonetes 

 (Table 11). 



Blinded animals show a direct effect by which the melanophores 

 are more expanded the brighter the light, but never as much as in 

 normal animals on a black background in the same light (Table 12). 



If different groups of the ommatidia in the sessile compound 

 eyes of these animals are illuminated separately, either by painting 

 over part of the eye with opaque varnish (which affords a. good 

 class demonstration) or by exposing the animals in specially 

 constructed boxes which admit light only to certain narrowly 

 delimited retinal areas (D, L, and V, Figs. 3-20 and 3-21), the 

 effects shown in Table 13 can be obtained. 



It is concluded from these and other observations that two 

 antagonistic hormones are involved : a Lz^/<2-darkening hormone, 

 LDH, normally stimulated by direct light on area D to cause 

 dispersion; and a Lz^/a-lightening hormone, LLH, stimulated 

 by reflected light on areas L and V to cause full concentration. 

 When the whole eye is illuminated both are secreted, but LLH 

 overrides LDH to produce almost complete concentration. A 



Table 12. Changes in melanophore index in ligia 



All index values are an average of measurements made on the posterior part of 

 the body of 24 specimens (from H. G. Smith, 1938). 



balance between the two hormones produces an intermediate 

 effect (Fig. 3-21^). The sources of the two hormones have not 

 been fully determined, but Kleinholz (1937) showed that removal 

 of the whole head is followed by dispersion, and extracts of the 

 head cause concentration of the melanophores. The source of 



