306 JAMES EDWARD ACKERT 



are numerous, and appear to be scattered about promiscuously. 

 Their form is very variable. They may be spherical, oval, elon- 

 gate and slightly spiral, heart-shaped,' pear-shaped, raggedly 

 lobulate, and with or without processes (fig. 5). In size they 

 vary from 34)u in length and 25.5ju in width to 374iu in length and 

 60ju in width. The cell body is filled with fine brown granules. 

 In hematoxylin-eosin preparations a few of the granules usually 

 take the dull blue stain of the hematoxylin, while in the methyl- 

 ene blue material some or all of the granules may stain a bright 

 blue. Figure 5, h represents a pigment cell containing stained 

 and unstained granules. 



2. Flying and interfemoral membranes 



The flying membrane of bats is a skin duplicature formed by 

 the lateral extension of the dorsal and ventral integument of the 

 body. The proximal parts of the membranes are covered with 

 fine hairs similar of those of the pelage, while over the distal 

 areas extremely fine, more or less modified hairs occur sparsely. 

 In the natural condition there is a manifold wrinkling and plait- 

 ing due to numerous elastic bands within the membrane (Schobl) . 



Externally the flying membrane is made up of small, hexag- 

 onal, plate-like cells which form a continuous membrane. Each 

 cell contains pigment granules which are collected into an intra- 

 marginal zone much as Schobl has described (p. 4). This in- 

 vestigator reports that the center and border of the cell (in 

 Vesperugo serotinus) are free from pigment granules. In Myotis 

 lucifugus and M. sublatus the writer found pigment in both of 

 these regions, but in smaller quantities than in the intra-marginal 

 zone. The cells of the outer (dorsal) surface of the flying mem- 

 brane contain more and darker pigment granules than do those 

 of the inner (ventral) surface (Schobl). In fact this surface in 

 places contains almost no pigment. 



As in the integument of the body the epidermis of the flying 

 membrane stands out in the sections in contrast to the cutis. 

 The Malpighian layer also can be readily distinguished from 

 the stratum corneum. According to Schobl's studies the Mai- 



