Witson and Marrin— Rod-like Tactile Organs in the Muzzle of Ornithorhynchus. 193 
We have also examined the mucous membrane covering the anterior portion of 
the snout of the Echidna and of the palate of this animal; but no such organs are 
present. 
The organs, the general appearance of which is well shown in fig. 3, Pl. xxiv., 
which is a photo-micrograph of a vertical section stained with logwood and eosin, are 
remarkably like the roots of hairs surrounded by their follicles, but possessing no 
papille. The core is seen to be both longitudinally and transversely striated, which 
still further adds to the resemblance. Directed towards the base of the organ a 
thick leash of nerve-fibres is seen, some of which end in from two to six small 
Pacinian-like bodies, which are here situated in apposition with the flat base of the 
re d-organ. 
These Pacinian-like corpuscles, together with the general nervous arrangement 
of the organs, will be discussed later. This rod-like organ is surrounded in its 
superficial half by the cells of the general epidermis, from which, however, it 1s 
sharply differentiated, as those epidermal cells which come into apposition with it 
are turned up so as to le with their long axes in a direction almost vertical to the 
surface. They thus form a kind of follicle enclosing the rod, and are no doubt forced 
into their upright attitude by the upward growth of the rod (figs. 3 and 4, Pl. xxv. ; 
fe. 8; Pl xxv.; and fig: 15, Pl. xxvz.). 
In its deeper half the organ is surrounded by the dermal tissues, the fibrous 
tissue of which is arranged around it in a circular manner, so as to form a definite 
sheath (fig. 13, Pl. xxv.). Such a relationship with the tissues of the cutis is probably 
occasioned by the epithelial downgrowth which forms the rod causing a depression in 
the summit of a dermal papilla. 
The epithelial elements composing the shaft of the organ are arranged in three 
concentric layers, as may be seen in fig. 15, Pl. xxvi., which is a semi-diagrammatic 
representation of a vertical axial section, or in the photo-micrograph of a transverse 
section of the organ, in its passage through the epidermis (fig. 6, Pl. xxiv.). In this 
latter the three rings of nuclei belong to the three layers. 
The innermost layer, whose elements constitute the core, is made up of a number 
of superimposed imbricated epithelial lamine, each of which is in the shape of a 
hollow truncated cone. These elements are compound and made up of three or more 
nucleated cells, but we have been unable to discover any differentiation between the 
component cell-bodies, and have come to the conclusion as to their compound nature 
on account of their possessing three or four nuclei, which nuclei form the most 
centrally disposed group, seen in the photo-micrograph of a transverse section, already 
referred to. 
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