Figure 1.
A Sapphirina metallina copepod under a dissecting microscope and transmitted illumination.
A: With a depolarizing light and no polarizing filter. B: Between two linearly polarizers at 45° to each other, showing body structure and polarization active (depolarizing, phase retardance, or birefringence[24]) structures. C: The animal between crossed linear polarizers showing only linearly polarization-active structures. Such linear polarization activity can arise from change in orientation of polarization, depolarization, or the creation of CP. D: Circularly polarized light passing through a copepod, according to its left or right handedness. Incoming light was depolarized. Arrows indicate areas of relatively strong CP, though not more than 30%; dark and bright areas indicate right and left CP, respectively. Note that most of these areas, such as eye tubes or posterior parts of carapace, do not show up when placed between crossed linear polarizers (insert C) suggesting that the process causing the CP under depolarized illumination, is not mere retardance such as by muscle fibers.
Figure 2.
Maps of the modulation depth of the signals through a Sapphirina copepod, when incoming light is linearly polarized, as detected by a CP detector.
A modulation depth of 1.0 indicates that all measured light is CP, whereas 0 signifies no CP. A: Each image is for a different orientation of the entrance polarizer, and therefore, of the illuminating beam, in 20° steps. The orientation for 0° was arbitrarily set. Note that CP handedness is not recorded. Locations of CP activity correspond with both muscles fibers as illuminated in Fig 1C and areas of CP created under depolarized illumination as in Fig 1D. B: The modulation depth as a function of the input polarization orientation at six locations on the animal is indicated in the figure inset.
Figure 3.
A: frontal section of dorsal integument showing the multilayer membrane structure, a honeycomb arrangement, in which the first stack layer is parallel and some of the other layers are rotated on their sides showing a layered pattern. B–C: Sagittal sections of the membrane structure showing the two different membranes.
Figure 4.
Outline of the system used to detect transmitted CP.
Illuminating light passed first through a depolarizer, and then, if needed, it was linearly polarized. After passing through the specimen, depending on handedness, the light was or was not filtered through a rotating 1/2 λ retarder that covered half of the field of view. The circularly polarized light was then linearized by a 1/4 λ retarder and an analyzer was used to examine it.