HAIR STRUCTURE OF THE MONOTREMATA 479 
Summary for Ornithorhynchus 
Ornithorhynchus anatinus possesses six well-defined areas upon 
the body, each of which is characterized by the growth of a dif- 
ferent kind of hair. These different kinds, or varieties, have, 
apparently, judging from the form of- the cuticular scales and 
medulla, been derived from two structurally distinct types of 
hair, the fur hair and the shield hair. 
The shield hair, because of its structure, acts as a protection 
against physical injury to the skin and precludes the entrance of 
water, while the fur hair serves as an insulating medium, guard- 
ing the body against changes in temperature. 
THE HAIR AND SPINES OF TACHYGLOSSUS (ECHIDNA) HYSTRIX 
The hair and spine types of Tachyglossus (plates 3 and 4) 
The first systematic account of the body covering of Tachy- 
glossus was given by Meijere in 1894, and in 1898 an account 
virtually similar, but with especial consideration to the disposal 
of the groups of hairs and spines, was published by Rémer. Dur- 
ing 1898 also, Spencer and Sweet had issued their work on the 
development of the hairs and spines in the monotremes and mar- 
supials, in which a careful study is made particularly of the de- 
velopment of the new hairs and spines and of the various follicu- 
lar layers taking part in their growth. 
Toldt (05), in a discussion of the genera which he maintained 
as Proechidna and Tachyglossus, was the first to suggest that 
the criterion of hair structure and form is, at least as far as these 
genera are concerned, significant from the standpoint of their 
phylogenetic study, and may be used as aids in determining the 
position of the species. In 1906 he described the hair and spine 
covering of a species allied closely to the one now under considera- 
tion, Zaglossus bruijjnii bruijjnii. 
A further contribution to the knowledge of the growth and 
development of the hairs and spines, with especial emphasis upon 
their grouping in the skin, was made by Pinkus in}1906. 
The body covering of Tachyglossus has been commonly de- 
seribed as of two types, spines and hairs. This is, however, a 
