HIPPOLYTE VARIANS. 627 



worth while noting that the "blue spots/' plainly visible 

 during the height of the nocturnal phase^ are during this 

 period clearly continuous with the general blue reticulum, 

 being connected therewith by branches which radiate from 

 the centres of the blue spots across their clear surrounding 

 "halos." As the recovery to the diurnal tint progresses, 

 these branches become red and join the now red network. 



The blue substance has the homogeneous appearance of a 

 pigment in solution. It takes but a limited share in the 

 coloration of the prawn during the day. The ventral denser 

 sheath of " chromatophores " and, in many specimens, the 

 thoracic limbs are the portions in which it chiefly persists 

 in the diurnal phase. It is interesting to note in connection 

 with the general lower light-intensity during the winter, that 

 more blue is observed in the same colour varieties of Hippo- 

 lyte varians during December than in July and August. 

 Whether, however, all the blue of a nocturne consists of 

 pigment extruded from the " chromatophoric " centres in 

 which it is stored during the day : or whether there is an 

 actual transformation of one or all the other pigments into 

 blue, are difficult questions. Extracts of five brown specimens 

 and of five brown ones in the full nocturnal phase in equal 

 quantities of 90 per cent, alcohol gave approximately simi- 

 larly coloured (red) solutions. This tends, as far as it goes, 

 to show that the red and yellow pigments are not metamor- 

 phosed. But more suggestive of a similar conclusion are 

 Exps. 1 and 2, Tables I and II, showing that the nocturne 

 may pass in a remarkably short space of time over into the 

 diurnal phase and back again to the nocturnal one. We have 

 nothing, however, to say here concerning the difficult matter 

 of the origin and relations of the pigments, though we hope 

 subsequently to follow up this as well as some of the many 

 other lines of investigation to which these colour-phenomena 

 point (see Newbigin, 1897, 1898, and authorities quoted). 



So far we have dealt with the natural nocturnal colour in- 

 duced by darkness. We must now consider certain means by 

 which the assumption of the nocturnal phase may be hastened 



