484 LEON AUGUSTUS HAUSMAN 
which may be suggestive of the configuration of the fused cells. 
Similarly, when a spine is broken obliquely across, the irregularity 
of the fracture of the broken cortex element may also be indica- 
tive of the original cell form (fig. 98, B.CO.), though it may be 
that these cortical cells have lost all originality of contour and 
have completely fused into a truly homogeneous substance. At 
present no statement can be made regarding their form in the 
various hairs and spines. 
While it is not within the province of this paper to discuss the 
development of the hairs and spines, from what has been observed 
it may not be amiss to call attention to the supposition that the 
different varieties of hairs and spines of Tachyglossus may have 
been derived from a single hair type, possibly of the wavy va- 
riety, by an increase in the thickness of the middle portion of the 
shaft. Their development can be determined with certainty, 
however, only by a’careful study of the stages of their growth 
from the follicle in the embryo and young. 
Summary for Tachyglossus 
In all essential respects the hairs of. Ornithorhynchus and 
Tachyglossus are similar. The curious flattened type of hairs is 
the characteristic form for this order. In both Ornithorhynchus 
and Tachyglossus this type comprises about 50 per cent of the 
body covering. In Tachyglossus the suggestion is advanced 
that the spines are developed from the wavy hairs. Not only in 
structure, but also in development are the hairs of Ornithorhyn- 
chus and Tachyglossus alike. Spencer and Sweet observe, ‘‘So 
far as essential points are concerned, the development of the 
large and small hairs alike agrees in both Ornithorhynchus and 
Echidna [Tachyglossus].”’ 
The type of hair, therefore, characteristic of the Monotremata, 
is the flattened type, represented by the shield hairs of Ornitho- 
rhynchus and by the flattened wavy and spiny hairs of T'achyglos- 
sus. On the other hand, the fur hairs, found in Ornithorhynchus, 
but not present in Tachyglossus, are like the general type of 
cylindrical fur hairs possessed by the majority of the mam- 
