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INTEGUMENT OF NECTURUS MACULOSUS 515 
quite evident. They are closely associated and usually occur 
in successive horizontal sheets, the fibers of adjoining layers 
running approximately at right angles to each other, so that in 
sections perpendicular to the surface cut ends and longitudinal 
views of fibers are seen in fairly regular alternation (figs. 6, 12). 
Some regions show these lamellae slightly interwoven. At 
certain points bundles from the compact horizontal sheets turn 
both outward and inward to join the vertical strands which 
pass upward from the subcutaneous region. Upright bundles 
are usually accompanied by blood-vessels and nerves going to 
the outer layers. 
The middle layer (drm.'’) is the most variable of the three, 
both in thickness and in the arrangement of its elements. In 
this intermediate region, composed of loosely woven bundles of 
connective tissue, the majority of the glands are imbedded. In 
fact, this layer seems to have been differentiated chiefly to pro- 
vide accommodation for these glandular structures, which grow 
in from the epidermis and attain such enormous sizes (Gaupp, 
04; Schuberg, ’03. ’07, ’08). In contrast with the layers above 
and below it, this region contains many connective-tissue cells, 
resembling in this the inner subcutaneous tissue. This stratum 
also receives bundles of fibers from both compact layers, but in 
regions where it is greatly thickened they cannot be traced very 
far. In regions where the glands are small and the intermediate 
layer is accordingly reduced, as on the side of the tail, bundles 
can be traced from their origin in the inner layer up over the 
bodies of the glands. 
Above this open spongy region there appears in sections a 
narrow, well-defined, clear zone, the outer compact layer (drm’). 
This region in other Amphibia, on account of its close relation 
to the epidermis and its clear appearance, has often been mis- 
taken for a basal membrane, especially by those who have worked 
on larval forms (Phisalix, 00a; Eycleshymer and Wilson, ’10). 
But Bugnion (’73), Paulicki (’85), and Schuberg (’03, ’07, ’08) 
have recognized that this layer is composed of connective-tissue 
fibers. In Necturus the composition of this region is quite 
readily determined. It is made up of sheets of fibers arranged 
