154 TUCKERMAN. [Vol. IV. 



frequently exceeds a millimetre in length, the transverse diam- 

 eter being only about 0.021 mm. Anteriorly the papillae are 

 longer and more delicate than elsewhere. As they near the 

 tip, however, they decrease in number and are somewhat 

 shorter. Posteriorly they frequently bear a recurved spine 

 (doubtless a transitional form) in addition to their more slender 

 secondary processes. Still further back, in some papillae, the 

 secondary processes appear to have coalesced, forming a single 

 stout, sharp-pointed, hook-like spine, as in many of the higher 

 Mammalia. Papillae thus modified are also sparingly inter- 

 spersed among the others at various parts of the dorsum. The 

 "secondary papillae form one or more incomplete rings at the 

 summit of the main upgrowth, leaving within a horseshoe- 

 shaped cavity. Where two rings exist, the inner one is usually 

 less complete than the outer. More rarely, within the inner 

 ring a few secondary papillae are irregularly scattered. The 

 secondary processes separate from the papillary body first in 

 front, those of the posterior side being given off at a higher 

 level. A few single filiform papillae, somewhat hair-like, are 

 scattered over the dorsum, particularly its anterior part. 



When lowly magnified, the main body of the papilla (in verti- 

 cal section) appears to consist largely of a mass of cells in the 

 form of a thick column or inverted cone. This mass is com- 

 ;iosed of several distinct but not always sharply marked layers. 

 The basal layer is quite thin, and consists of small but clearly 

 defined, deeply staining columnar cells. Succeeding this is a 

 very thick layer, consisting below of nucleated polyhedral cells, 

 and above of fusiform cells. The cells of this layer are largely 

 granular and stain readily in haematoxylin, but less deeply than 

 those of the layer underlying. Resting upon this layer, and 

 also covering the lateral area of the papilla, is one consisting of 

 elongated cells, more or less granular. These cells are some- 

 what attenuated below, and large and swollen above and at the 

 sides. The nuclei are not always readily distinguishable, but 

 are of unusual size. The cells are not stained by haematoxylin. 

 Against this layer is a comparatively thin one, likewise com- 

 posed of cells fusiform in shape. The cells stain deeply, and 

 are apparently of the same general character as those consti- 

 tuting the bulk of the secondary papillae. The entire free por- 

 tion of the secondary processes in the anterior dorsal region 



