Witson and Martin—Roa-like Tactile Organs in the Muzzle of Ornithorhynchus. 199 
Fig. 
5 
Fig. 
Fig. 
6.—Photo-micrograph of horizontal transverse section of rod-like organ in its superficial half. 
Hematoxylin stain. Zeiss’ 4 mm. apochromatic objective, projection ocular No.2. (Achromatic 
condenser). x 435 diameters. The innermost four to five nuclei are those of the conical epithelial 
lamine referred to in the text. In the area surrounded by these nuclei is to be seen a circular 
arrangement of white dots, which are the transverse sections of the axial group of nerve-fibrils, 
while external to the nuclei is a wider circlet of white dots, which are the peripheral series of 
nerve-fibrils. Immediately surrounding the latter is a circle of dark transversely elongated 
nuclei, which are those of the imbricated cell-elements marked m. in fig. 15. Outside this 
circle again is the thicker layer and polyhedral cells, enclosed in turn by the modified cells of 
the general epidermis, which are, however, at this level slightly interrupted by the very tips of 
the dermal papillary upgrowths surrounding the rod and here just cut across. 
PLATE Xxv. 
7.—Photo-micrograph of horizontal transverse section through the layer of Pacinian-like bodies 
immediately subjacent to the flattened base of a rod-organ. Anilin blue-black stain. Beck’s } 
inch objective, no ocular. x 200 diameters. Between and around the Pacinian-like bodies 
may be seen sections of medullated nerve-fibres on their way to enter the base of the rod. 
8.—-Photo-micrograph of vertical section, lower half of rod-like organ shown in fig. 3. Beck’s } inch 
objective, without ocular. x 200 diameters. To show the thick bundle of medullated 
nerve fibres ascending towards the base of the rod, two Pacinian-like bodies beneath the flat 
base of the rod, and a number of “lenticular” nerve end-organs embedded among the 
epidermal cells forming the base of the rod. In the shaft of the organ the longitudinal 
striation due to the presence of the axial and peripheral groups of nerve-fibrils is visible. 
9.—Photo-micrograph of vertical section of base of another rod-organ. Heematoxylin stain. Beck’s 
objective } inch, without ocular. x 200 diameters. Shows group of “lenticular bodies ” in 
base of rod and a Pacinian-like body in the dermis at some distance below the rod, and of 
larger size than those placed immediately under the base. 
Fig. 10.—Photo-micrograph of vertical section of base of another rod-organ. Freud’s gold chloride stain. 
Zeiss’ 3 mm. apoch. hom. imm. objective. Projection ocular No. 2. (Achromatic condenser). 
x 580 diameters. Shows two “lenticular bodies” in base, with horizontal dark stained line 
crossing each, due to the gold impregnation of the nerve disk or meniscus between the lens- 
shaped cell elements. Also nerve-fibres passing into base of rod to give off terminal fibrils. 
ig. 11.—Photo-micrograph of vertical section, basal portion of rod-like organ. Freud’s gold-chlovide 
stain. Zeiss’ 4 mm. apochrom. objective. Projection ocular No. 2. (Achromatic condenser). 
x 435 diameters. Shows more especially the medullated nerve-fibres entering the base of the 
rod and there losing their white sheaths, the axis cylinders breaking up into the terminal 
nerve-fibrils, which course peripherally through the shaft. Observe that the fibres which give 
off the peripheral group of nerve-fibrils enter the lateral aspect of the rod slightly above the 
base. 
Fig. 12.—Photo-micrograph of vertical section of rod-organ, broken about its middle. Hematoxylin stain. 
Zeiss’ D objective, compens. ocular No. 6. x 625 diameters. Shows bundle of varicose 
nerve-fibrils belonging to axial group projecting, antenne-like, from broken end of rod-like 
organ into empty space formerly occupied by peripheral end of rod. Observe that the fractured 
end of the core of the rod exhibits the profile-contour of one of the truncated conical epithelial 
elements figured semi-diagrammatically in fig. 16 (c). 
