610 SUMMARY OF CURRENT RESEARCHES RELATING TO 



determines the nature and extent of the pigment movements. " Reaction 

 to background " is traceable to the eye, and is probably a consequence 

 of an asymmetrical distribution of retinal pigment brought about not 

 by changes in the amount of light falling on the eye, so much as by 

 changes in the way in which light falls on the eye. 



The phenomena presented by the pigments are not exhaustively 

 interpreted by any " protective " hypothesis. The chromatophores are 

 centres of metabolic activity, and from them a nocturnal translocation 

 of a blue substance takes place. There is evidence that this blue sub- 

 stance is produced from, and at the expense of the diurnal chromato- 

 phore-pigments. The blue substance passes from the chromatophore- 

 centres, persists for a time in the body, and ultimately disappears. 



The chromatophore-system of Mysidean Schizopods is built on a 

 common plan — a primary system — to which colour-pattern is due. But 

 Decapod Crustacea possess a primary and a secondary system of chro- 

 matophores. The primary system appears in the embryo, is completed 

 in the Mysis stage, and persists throughout life, but takes no part in 

 colour-pattern. The secondary system arises in an early stage in 

 development, increases in extent throughout life, and produces the 

 colour-patterns of the adolescent and adult. The chromatophores of 

 the primary system are profusely branched, few in number, segmentally 

 arranged and centralised ; those of the secondary system are sparsely 

 branched, numerous, irregularly arranged and decentralised. 



The chromatophores of Mysidaj are multicellular organs. Those of 

 the neural group are developed from the epidermis, but losing this 

 connection acquire a close relation with the central nervous system. 

 The distribution of the primary chromatophore-system follows that of 

 the ganglionic parts of the nervous system. The chromatophores of 

 Decapods are plurinuclear connected structures, and their distribution is 

 not confined to the ganglionic parts of the nervous system. 



The primary systems afford assistance in the determination of genera 

 and species. They have taxonomic value both in early and late stages. 



As to inheritance, the several adult colour-patterns of Palccmon and 

 Crangon are constant and develop directly. The evidence tends to 

 prove that both secondary and primary chromatophore-systems are 

 inherited. The adult colour-pattern of Hippohjte cranchii is constant, 

 but develops indirectly. The adolescent possesses a special colour- 

 pattern, developed in large measure in relation with the primary system 

 of the zoasa. Both persist though concealed by the independently 

 developed adult pattern. In Hippolyte varians, several adult colour- 

 patterns occur. They develop indirectly. The primary system is the 

 same in all. The primary system is inherited ; the adolescent colour- 

 patterns are possibly inherited ; but the inheritance is immaterial since 

 the final goal is reached by any adolescent road ; that is, the adult 

 colour-pattern of Hippohjte varians is the result of environment. 



Statocysts in an Isopod.* — A. Thienemann describes the first case 

 of statocysts in an Isopod. He found two of these organs on the telson 

 of Anthura gracilis which creeps about between the shells of Balanus 

 improvisus. The organs are more primitive than those of Mysis ; thus 



* Zool. Anzeig., xxvi. (1903) pp. 406-10 (2 figs.). 



