1869. ] MR. F. H. WELCH ON LEPUS AMERICANUS, 233 
end and arranged in linear series in the long axis of the shaft, covered 
externally by a delicate tissue of elongated flattened epithelium (fig. 2). 
The shaft of the under-fur (fig. 1) averages =>, inch in thickness, 
has one series of cells in its structure; the pile, ;4, inch in diameter 
(fig. 3), four or more, according to the varying thickness of the shaft, 
Fig. 1. Microscopic aspect of shaft of under-fur. 
2. Epithelial covering of shaft. 
3. Shaft of pile. 
one series only at the tip, and the number gradually augmenting to 
the greatest cireumference—the cells varying in colour according to 
the portion examined, but when white to the naked eye then colour- 
less microscopically. The increase in the length of the autumnal 
hairs has been already noted ; to this must be added that the blanch- 
ing shaft, in the majority of cases, has also augmented in thickness, 
the average ~4, inch in diameter (corresponding to the new growth), 
the increase being consequent upon a more than usual number of 
series of cells entering into its composition. In some hairs where the 
centre of the shaft has changed, bounded on each side by an unchanged 
portion, it will be noted that at the altered segment the shaft bulges 
out, increasing in diameter from <4, to <4, of an inch by the addi- 
tion of one or more series of colourless cells, and that at the unaltered 
portion, both above and below, it is contracted to the former size, 
contrasting strongly both in the number of series of cells and in 
the absence of colour in the changed parts. If also we examine one 
of the long black hairs bleaching at the tip, the addition of the 
colourless cells, as contrasted with the same portion of an unchanged 
hair, is very marked. Again, a comparison of changed hairs with 
unchanged ones of almost equivalent length, from the same vicinity, 
gives frequently a double thickness to the former over the latter. 
The increase of series to the shaft of the hair in process of change 
seems the rule, the absence of colour invariable ; but in the whiskers, 
which in their structure approach rather the human hair with its 
fibrous cylinder and cellular centre, the former is not so apparent. 
