HAIRS OF MONOTREMES AND MARSUPIALS. 



551 



or five hairs in each bundle ; Welcker gives as many as fifteen 

 to thirty ; Poulton (p, 159) gives the number as varying 

 between seven and eleven, including both young and old hairs, 

 the greatest number of old hairs being ten, and, referring to 

 his figures, states that they " prove that, at any rate in the 

 dorsal region, Leydig's estimate of the number of hairs in a 

 bundle is too small, while that of Welcker is far too large." 



There is evidently a considerable amount of variation, 

 possibly between different individuals but more probably at 

 different times of the year, and this variation affects not only 

 the number of small hairs in each bundle but also the number 

 of bundles. On the dorsal area Poulton gives the latter as 

 constantly four. In the same part we have found the number 

 to be usually the same, but occasionally five and more rarely 

 even six bundles may be present. In his work dealing with 

 the arrangement of the hairs in various mammals, Meijere ^ 

 figures, on the back, two groups with five bundles each. 



With regard to the number of hairs in each bundle, the 

 following table represents an average series in a fully-grown 

 male examined by us ; in the case of successional hairs the 

 latter are represented with the sign + in front of them. 



Group 5. 

 Bundle — 

 1—16 

 2— 7 + 6 

 3—12 

 4—13 



These show the number of small hairs in each bundle to 

 vary generally from twelve to eighteen, less than twelve being 

 very rarely met with. 



Successional hairs are rarely met with, — there is, as Poulton 

 says, no difficulty in distinguishing them when they are 

 present, — and the few which are developing have not yet 

 reached the level of the common follicular opening of the 

 bundle. 



1 'Morph. Jahrbueh,' Bd. xxi, 1894, p. 312. 



