696 



Comparative Animal Physiology 



sion of white pigment. In Group III, on the other hand, there is a blacken- 

 ing of the whole bodv, although the white pigment remains broadly dis- 

 persed. These strikingly different results obser\ed for the animals of Groups 

 I, II, and III are explained in terms of differences in the responses of the 

 chromatophore systems to the eyestalk material, since reciprocal injections 

 demonstrate that extracts of eyestalks from specimens of other groups pro- 

 duce in the specimen of any given group a response qualitatively the same 

 as that produced by the specimen's own eyestalks. For example, eyestalk ex- 

 tracts prepared from animals of Group III lighten the body of animals of 



Fig. 263. The sinus gland of Cambarus and its innervation. A, Without, and B, with 

 sheath of optic gangHa removed. Sg, sinus gland; N, Sheath; SE, brain; CE, connectives; 

 OP, optic nerve; XO, X-organ; OCi and 0C>, oculomotor nerves; Fi fiber tract from brain; 

 Fi, fiber tract from medulla terminalis; L, Lamina ganglionaris; ME, medulla externa; Ml, 

 medulla interna; MT, medulla terminalis; AB, AD, AT, RL, and RM, eye muscles. From 

 Welsh, J. Exp. Zool., 86:35-49 (1941). 



Group I from which the eyestalks have been removed, and, conversely, eye- 

 stalk extracts prepared from animals of Group I darken eyestalkless speci- 

 mens of Group III. 



The source of the chromatophorotropins from the eyestalk is the sinus 

 gland (Fig. 263). This was postulated and strongly supported by Han- 



