556 



THE EYE IN EVOLUTION 



Insects is limited to a small number of species, and the mechanism whereby 

 it is achieved is relatively unexplored. The evidence suggests, however, that 

 the main source of the hormones is the cerebral ganglion since its extirpation 

 inhibits colour adaptation and the injection of extracts redistributes the 

 integumentary pigment [Carausius — Dupont-Raabe, 1949-51). The hor- 

 mones appear to be distributed through the agency of the corpora cardiaca 

 while the allata seem to be inactive in the process (B. Scharrer, 1952). In 

 some species the eyes are the sole receptors of the stimulation and their 

 occlusion or section of the optic tracts inhibits all responses (the stick 

 insect, Dixippus — Atzler, 1930). The diurnal rhythm in the migration 



COBDUS ALLATUM , 



COKOiJi CAQOJACUM 



rJCavUS COftPOK/S CAODIACI 



Fig. 726. — The Neuro-secretory System of an Insect. 

 A general diagrammatic representation (B. and E. Scharrer, 1944). 



of the retinal pigment of some species suggests that here, also, an endocrine 

 control may be active ^ (the noctuid moth, Plusia gamma — Kiesel, 1894 ; 

 the beetle, Bolitotherus cornutus — Park and Keller, 1932). 



The important gonadotrojjic hormones controlUng reprodvictive processes and the 

 development of the sex organs are elaborated mainly in the corpora allata which in 

 some species may be under the control of the cerebral ganglion (Altmann, 1952 ; B. 

 Scharrer, 1952), while the complicated processes oi growth, moulting and differentiation 

 with all their spectacular changes are integrated by hormones mainly elaborated 

 in the prothoracic gland. ^ Metabolic processes such as oxygen consumption are effected 

 through the pars intercerebralis and the corpora allata (Thomsen, 1949-52). 



THE NEIJRO-ENDOCRINE SYSTEM OF VERTEBRATES 



The neuro -endocrine mechanism of Vertebrates is centred in the 

 extrenH'ly complex aggregation of nuclei and secretory organs known as the 

 hypotlia-mio-hypophyseal system ; from the hormonal point of view the 

 most interesting section in this part of the central nervous system is the 



1 p. l!i 

 ^ Revie, 



ee Wigglesworth, 1934-40 ; Bodenstein, 1942 ; B. Scharrer, 1953. 



