Colours are not Qualifications of Light, derived from Refractions, or Reflections of natural Bodies (as 'tis generally believed), but original and connate properties, which in divers Rays are divers.
As the axis of the ctenidium lies by the side of the body, and is very frequently connate with the body, as so often happens in Gastropods also, we find it convenient to speak of the two plate-like structures formed on each ctenidial axis as the outer and the inner gill-plate; each of these is composed of two lamellae, an outer (the reflected) and an adaxial in the case of the outer gill plate, and an adaxial and an inner (the reflected) in the case of the inner gill-plate.
Other distinct kinds are P. campanulatus, 12 ft., pale rose, of bushy habit; P. humilis, 9 in., bright blue; P. speciosus, cyananthus and Jaffrayanus, 2 to 3 ft., all bright blue; P. barbatus, 3 to 4 ft., scarlet, in long terminal panicles; P. Murrayanus, 6 ft., with scarlet flowers and connate leaves; and P. Palmeri, 3 to 4 ft., with large, wide-tubed, rose-coloured flowers.