198 Macrteay MemoriaL Vouume. 
specimen of Orxithorhynchus, and to Prof. Anderson Stuart for his courtesy in 
placing at our disposal well-hardened specimens of the snout of Echidna for 
comparative study. 
In the production of the illustrations which accompany this paper we have to 
express our large indebtedness to Mr. Robert Grant, the able assistant in the 
Physiological Laboratory, with whose photo-micrographic camera, and with whose 
valuable assistance, some of our best photo-micrographs were obtained. Much 
other incidental aid in the preparation of the illustrations has been rendered us by 
the same enthusiastic helper. 
EXPLANATION OF PLATES. 
PLATE XXIV. 
1.—Photo-micrograph of vertical section of lateral margin of snout (“upper lip”) of Platypus. 
Kultschitzky’s stain. Zeiss’ 70 mm. objective without ocular. x 12 diameters. Cf. key 
drawing, fig. 14, Pl. xxv1. 
Fig. 2.—Photo-micrograph of vertical section of skin of snout of Platypus. Picrocarmine stain. Beck’s 
2-inch objective without ocular. x 70 diameters. Shows general view of epidermis in section, 
including vertical section of two rod-like organs. 
g. 3,—Photo-micrograph of vertical section of rod-like organ and neighbouring epidermis. Hematoxylin 
stain. Zeiss’ objective A, compens. ocular No. 6. x 135 diameters. Shows general view of 
structure of rod-organ, with thick leash of nerve-fibres passing to it in dermal tissues, and two 
Pacinian-like bodies at its flattened base. 
Fig. 4.—Photo-micrograph of superficial half of the rod-like organ shown in fig. 3. Zeiss’ objective D, 
compens. ocular No. 6. x 625 diameters. The shaft of the rod is best defined in the 
lower part of the figure, where the different layers are easily distinguishable (see fig. 15 for 
semi-diagrammatic representation of the various elements). The comparatively wide and 
striated core of the shaft is constituted by the structures marked c. in fig. 15, and corresponds 
to the whole space in fig. 15 between the two lines marked p.f. This core is seen to be bounded 
by a well-marked layer with deeply stained nuclei, constituted by the imbricated cell-elements 
marked m. in fig. 15 ; while immediately external is the layer of large polyhedral cells marked 
p. in fig. 15. Outside this layer in the upper part of the photo is the layer of slightly modified 
cells of the general epidermis, marked e. in fig. 15, and in the lower part of the photo also is a 
somewhat irregular layer of slightly modified epidermal cells, outside which are found the 
dermal tissues, which completely surround the lower half of each rod. 
Fig. 5.—Photo-micrograph of vertical section of middle part of rod-like organ, fixed in Flemming’s fluid 
and unstained. Beck’s objective 2 inch without ocular. x 200 diameters. To illustrate 
structure of shaft of rod-like organ. 
