OF THE ORNITHORHYNCHUS PLATYPUS. 
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Lastly, the ductus cochleae is almost straight in the Bird, whereas in the typical 
Mammal it is spiral, and even in the Ornithorhynchus it is coiled round at the apex. 
Similarities :— 
The membrana basilaris and membrana tectoria are very much alike in both types of 
cochlea. Also the mode of distribution of the nerves, including the ganglionic mass. 
But more important than these is the presence of a lagena with its vestibular-like 
nerve epithelium, which is found at the apex of the cochlea both in the Ornitho- 
rhynchus and the Bird, but not in that of the typical Mammal. 
General resume. 
1. That although the general form of the cochlea tube of the Ornithorhychus is like 
that of the Bird (as it is almost straight and of equal size throughout, instead of 
being a tapering spiral), yet its internal arrangement and microscopical structure is 
unmistakably Mammalian in type. 
2. That the acoustic apparatus of the organ of Corti is not nearly so extensive as 
in typical Mammals, nor do the various minute structures forming it appear to be so 
well developed. 
3. That the cochlea of the Ornithorhynchus possesses an addition (the lagena) to 
its membranous labyrinth which is also found in the Bird, but which is not found in 
the ordinary Mammal. And thus the presence of this lagena may be looked upon as 
another of the many links between the Bird'"' and Mammal which are found in this 
Monotreme. 
Mode of preparation adopted in this research. 
For obtaining thin sections of this cochlea I made use of the same mode of 
procedure as described in my paper on the organ of Corti in Mammals, read before 
this Society in 1876, which is briefly as follows :— 
The tissues were hardened in an alcoholic solution of chromic acid; the bone 
decalcified in a dilute (f per cent.) solution of nitric acid aided by almost constant 
movement of the tissue, by means of an ordinary meat roasting-jack. 
Saturated with gum-water, then dehydrated in alcohol, imbedded in parafin, cut by 
a razor in a Stirling’s machine. Variously stained and mounted. 
In order to obtain a correct idea of the relation of the parts, I mounted the sections 
of certain cochleae in their proper order throughout; this I did with sections cut 
transversely and longitudinally, in the former case cutting the cochlea into about 120 
sections, and in the latter making about 10 thicker ones. By this means, aided by 
* Bat it must be borne in mind, as already stated, that the Bird’s cochlea is similar to that of Reptiles 
and Amphibians ; and therefore this lagena is really a link between the cochlea of the higher and lower 
vertebrates, and not merely between that of the Mammal and Bird. 
