Fig. 1. Bright and dark camouflage reactions. The subjects were 28 mm A.tigrinum larvae. Skin incisions produced the slight discoloration of the animals' heads. Primary magnification: x 7.6.
Fig. 1. Bright and dark
camouflage reactions. The subjects were 28 mm A.tigrinum larvae. Skin incisions
produced the slight discoloration of the animals' heads. Primary magnification:
x 7.6.
Fig. 3. Integumentary melanophores. This micrograph shows the partially
darkened skin of an A. tigrinum larva maintained in a transparent bowl up to sacrifice. The
dark spots deep to the epidermis are dermal melanophores, the principal
mediators of the camouflage reactions and the end points of the present
investigation. With further darkening the 'spots' give the appearance under the
dissecting microscope of expanding and eventually coalescing into a confluence
of tigroid patches. In brightening the reverse occurs, the areas between
light-absorbing foci progressively increasing as the spots become punctate. The
changes observed with the dissecting microscope may actually represent
redistributions of melanosomes within essentially fixed cytoplasmic processes
(2). The soma of a single epidermal melanocyte may be seen on the left of the
micrograph, as a dark dot among the subsurface epithelial cells. In the
stereomicroscope epidermal melanocyte somata appear as minute, widely separated
puncta. Several stellate processes extend from each epidermal melanocyte,
insinuate between the epithelial cells and collectively form a delicate
meshwork. The meshwork darkens or becomes transparent as melanin granules move
into or out of the processes. The latter events were observed with the phase
microscope during preliminary investigations. Epidermal melanocytes finely
modulate the skin's reflections; they can do so independently of changes in the
dermal melanophores. While only the latter cells were exploited for the present
investigation, it is worth noting that dispersal of pigment into the processes
of epidermal melanocytes may give a false impression of darkening when the
subject is observed with the naked eye. {For an electron micrographic view of the dermal melanophore, go here.}Primary magnification: x 97.5.
Fig. 4 shows the partially expanded melanophores of an A. punctatum
larva exposed in a polycarbonate tumbler to light from a circular horizontal
source. The small cells in the plane of focus are epidermal melanocytes that
may serve in this plate as a rough gauge for the dermal melanophores (arrows),
the larger spots slightly below the focal plane and therefore somewhat fuzzy,
here. What fig. 4 exhibits is typical of stock animals reared in transparent
receptacles. Fig 5 is a subject that was paired with that of Fig. 4 but
vertically illuminated in a white cup, in the standard light chamber. The two
photographs were taken within moments of each other, 2 days into a 7-day
observation period. What is seen in 4 and 6 remained constant during the latter
interval.
Figures 6 and 7 show the effects of exchanging the experimental conditions,
i.e., swapping the places of the two subjects. Fig. 6 is the subject of Fig. 4
but 24 h after transfer into a white cup and to the standard light chamber;
Fig. 7 shows the effects of the exchange on the subject in Fig. 5. Primary
magnification: x 40.
Fig. 8a. Macrograph of A. punctatum larvae 5 weeks after surgery. From left to
right: unoperated, cyclops-I. triclops, eyeless. This cyclops-I exhibited no
camouflage reactions; its eye atop the head is barely visible because of the
deep pigmentation of its skin (compare it with the eyeless animal on the
right).
Fig. 8b
Macrograph similar to 8a. From left to right: one-eye, triclops, eyeless, unoperated and a cyclops-II whose ectopic eye can be seen (see Fig. 9 for better perspective on the latter).
Fig. 9. Macrograph of A. punctatum larvae 5 weeks after surgery. From left to right: cyclops-II, eyeless, unoperated. This cyclops-II exhibited normal camouflage reactions from 25 days onwards after the transplantation.
Fig. 10a. Macrograph of A. opacum larvae, 6 weeks after surgery, showing a cyclops-II, upper right (2 o'clock); one-eye, at 3 o'clock; eyeless, lower left (7-8 o'clock). Beginning about one month postoperatively, and thereafter, this cyclops-II, showed the normal camouflage reactions. The white spots, in the tail and body of both the one-eyed and cyclops-II subjects, are guanophores, which are obscured during darkening. Notice also the pigmentation especially of the hind legs. See Figs. 10b closer views of the cyclops-II.
Fig. 10b
Fig. 10b Cyclops-II from 10a. The photo has been rotated and slightly enlarged to show the cocked eye on the cyclops-II. Notice also the head of the one-eye in the upper left-hand corner.
Fig. 12. Optic nerve and chiasm of a 45-mm A. tigrinum larva, unilaterally enucleated approximately one month prior to fixation but otherwise normal. This specimen was used in preliminary analyses conducted to design the lesions. The removal of one eye facilitated the tracing of optic fibers through the optic chiasm (near the center of the micrograph); a small portion of the retina appears in the upper right corner; the occipital pole of a cerebral hemisphere is just visible about 15 mm off the upper left corner. The ependyma- like formation anterior and just deep to the optic nerve root is mainly the ventral extreme of Bellonci's nucleus (see especially refs. l and 15). This section is nearly tangential to the dorsum of the head. Almost ascertainable in the micrograph is the fact that, upon decussating, the optic nerve fibers sharply bend out of the plane of sectioning (the crossing fibers turn dorsally here). Bodian's protargol stain. Primary magnification: x 39.6.
Fig. 13. Dissected, glycerinated head of an A. tigrinum larva, inflicted with incisions I+II, as seen from the ventral perspective. To enhance contrast, region A was removed from the dissection; the mucosa was stripped from the roof of the mouth and oropharynx; the rostral end of the specimen was tipped up. The lower arrow points to incision II The upper arrow points to the location of the roots of cranial nerve III, which was visible in the dissection but of insufficient density to show in the photograph; nerve III marks the surface location of the peduncle. The obliquity of the perspective spuriously exaggerates the actual amount of tissue anterior to plane I. The optic chiasm and postchiasmal commissure contribute to the transverse mid line opacity deep to the optic nerve roots. The opaque masses in the lower part of the photograph, on either side of the medulla, are the endolymphatic sacs. The roots of nerves V, VII and VIII can be seen near the sacs. Primary magnification: x 21.12
Figs. 14-17. The animals in 14 and 15 were eyeless and sham-operated, respectively, in the volley containing the subjects in Figs. 16 and 17. The subjects of Figs. 16 and 17 exhibit the normal bright reactions of two incision I subjects in white cups. Primary magnification: x 16.6.
Fig. 18. Parasagittal section of the brain of an A. punctatum larva inflicted with incision I directly through the skin (a non- standard operation) and fixed 5 days thereafter. The arrow on the left points toward the optic nerve; the one on the right indicates the ventral extent of the lesion penetrating to the exterior of the brain. The epithelium had already healed over the head wound. This animal retained normal camouflage reactions. Hematoxylin and eosin staining. Primary magnification: x 32.5.
Fig. 19. A specimen in the same operative group as the subject in Fig. 18. The arrow at the lower central portion of the photo, and furthest to the right of all shown, points toward the optic nerve. The other arrows, those curving dorsoventrally (up in the photo) mark the lesion passing posterior to the plane of the optic chiasm. This animal was fixed concurrently with the one in Fig. 18. When placed in a white cup after surgery, the subject immediately began darkening and showed no signs of a bright reaction thereafter. Hematoxylin and eosin staining. Primary magnification: x 32.5.
Fig. 20. Horizontal section of the head of an A. punctatum larva one week after hemisection through plane II. Incision II often disrupted the topography of the region. Hemisections with a limb inserted as a marker were used to verify the location of the lesion and thus gauge the distance of plane II from other structures. In the photograph, a segment of upper arm can be seen at the lower arrow; measurements were taken on the unsectioned (and thus undistorted) side here. The upper arrow points to the mesencephalic ramus of the cerebral carotid artery which passes close to the oculomotor nerve and also marks the surface location of peduncle, some 250-400 um anterior to II, the precise distance depending on the size of the subject. Hematoxylin and eosin staining. Primary magnification: x 48.
Fig. 21. Parasagittal section of the brain of an A. punctatum larva exhibiting incision II (total transection) from a lateral perspective. The left-most arrow shows the ventral extent of the lesion. The right arrow points to the optic nerve. The middle arrow indicates the infundibulum and, above the latter (in the photo), the plane of the peduncle. Hematoxylin and eosin staining. Primary magnification: x 33.5.
Figs. 22 and 23 illustrate the reactions of two incision II subjects, the left member of the pair to a white cup, the right one to a black container. The two photos were taken 6 days postoperatively, 11 hours into the daily light-on duty cycle and during the same session as those of Figs. 24 and 25. Primary magnification: x 16.2.
Figs. 24 and 25 (left and right). The subject on the left shows the darkening effects of lesion (incision) I+II; the animal was maintained in a white cup for 6 days before the photo. The subject in 25 (right) had its region B removed; it was maintained a white cup for 6 days prior to the photo. These two animals and those of 22 and 23 were sibling A. opacum larvae. Primary magnification: x 16.2.
Figs. 26 and 27. These are 28 mm A. tigrinum larval siblings. The left member is an unoperated control in a white cup. On the right is a tectectomized animal also in a white cup. The head wound is visible in 27. Photo taken on morning after surgery. Compare with 28 and 29. Primary magnification: x 16.2.
Figs. 28 and 29. These are 28 mm A. tigrinum in same experimental run as 26 and 27. The left member (28) is unoperated, the right tectectomized, both being dark tested. The head wound is visible in 29. Photo taken on morning after surgery. Compare with 26 and 27. Primary magnification: x16.2.
Fig. 30. The brain of an A. punctatum larva inflicted with lesion 5 (see Fig. 2) and fixed on the day after the operation. The minute concrescence above the left arrow, ependyma of the preoptic recess, may orient the reader. Barely visible in the photograph, but identifiable in the section, are the optic chiasm and postoptic commissure, deep to the still-intact mucosa above the left arrow. The right arrow points to the lesion where the pharyngeal mucosa had not yet healed. A thin, dark line -- intensely basophilic extracellular material closely holding together the cut surfaces of the medullary substance -- indicates the course of the incision through the root of the infundibulum. Dorsal to the latter is a rift in the peduncular gray matter (upper arrow). Subjects with this lesion quickly and permanently lost the bright reaction. Hematoxylin and eosin. Primary magnification: x 32.5.
Figs. 31 and 32 show the loss of the dark reaction following removal of B (left) or hypophysectomy alone. Compare with 33 and 34. Primary magnification: x 16.2.
Figs. 33 and 34. Figure 33 (left) shows the recovery of the dark reaction following the implantation of a B region into a B-less animal. Figure 34 shows that the same results can be obtained by simply inserting a hypophysis into the subject's IIIrd ventricle. Compare with 31 and 32. Primary magnification: x 16.2
Five-step ratings of melanophores in the Hogben-Slome index, 1-5, from left to right [after Hogben and Slome, 14]:
Bright = 1-2; dark = 4-5; animals against a neutral background show and H-S index in the mid range (2.5-3.5)
A Fig. 40. Biclops (left) and a one-eyed A. punctatum sibling showing bright reaction.