SKIN AND REPRODUCTIVE ORGANS OF NOTORYCTES. 327 



tlie level of the liair-roots in tins modified region^ is a thick 

 layer of fat cells. The greater thickness of the dermis here 

 does not end abruptly, but gradually decreases from the 

 centre of the area till it reaches the margin, where there is a 

 small sudden decrease in thickness, marking the boundary of 

 the patch [cf . 8, pp. 45, 46] . 



The difference in thickness of the corneous layer in the 

 modified patch, and over the general body surface, is occa- 

 sioned by the compactness of this layer in the former case, 

 and its looseness in the latter. 



Hairs. 



As in Ornithorhynchus [cf. 7 and 9] and Echidna [cf. 9] 

 the hairs are of two kinds, large and small, arranged in 

 bundles (PI. 19, figs. 1 and 3) containing usually one large 

 and a greater number of small hairs [cf. 8, pp. 45, 46]. The 

 hairs of each bundle have a common neck and opening (figs. 

 2-4, c.f.o.) to the surface, where the individual follicles are 

 absent. 



The bundles are furthermore arranged in groups of three 

 (PI. 19, fig. 1), or sometimes four or even five, in more or 

 less straight lines, each bundle, however, having its own 

 follicular opening not communicating with that of the other 

 bundles in the group (see PI. 19, fig. 2), so that in trans- 

 verse sections near the surface, the group arrangement is 

 often lost. 



The arrangement at deeper levels is shown in PI. 19, 

 fig. 1, where we have a typical group of three bundles from 

 the skin of the back. The number of small hairs in each 

 bundle varies from nine to twenty, the most numerous 

 examples showing from eleven to nineteen. Occasionally 

 the large hair seems to be absent. As will be seen, there 

 are in the group figured — 



{Bundle 1. 1 large hair and 15 small hairs. 

 „ 2. 1 „ „ 13 „ 



jj 3. 1 ,, „ 12 „ 



VOL. 51, PALtT 2. NKW SEKIES. 24 



