waite: antennal glands in homakus amekicanus. 167 



The muscular layer is more variable in thickness than is the epithelial 

 layer. It is composed of long spindle-shaped cells (Fig. 12) of different 

 lengths, containing centrally located nuclei. The cells and nuclei are 

 much flattened in one plane. The edge of the cell is frequently crinkled 

 so as to produce a sinuous outline (Fig. 13). The cell contents are 

 fibrillar, as is well shown when a cell is frayed out in teasing. The 

 fibrillae are likewise crinkled. There is usually present an axial bundle 

 (Fig. 13, fas. ax.) of fibrillae, which seem to be more closely bound to- 

 gether than are the others ; these stain with hematoxylin more deeply 

 than the rest of the cell. The thickness of this muscular layer varies. 

 It may be several cells (Fig. 10, la. mu.) or a single cell deep (Fig. 11, 

 la. mu.), or it may disappear altogether, as it does where the wall of the 

 vesicle is attached to the dorsal face of the endsac (Fig. 2, par. vs.). In 

 any given place in the muscular sheath the cells lie parallel with one 

 another, there being no crossing or formation of meshwork. 



Between the basement membrane of the epithelium and the muscular 

 sheath there is a layer of connective tissue containing a plexus of blood- 

 vessels. One of these is seen cut crosswise in Figure 11 (vas. sng.). 

 These vessels present the ordinary structure seen in the vessels of other 

 parts of the body, and are readily distinguishable from the two other 

 layers of the wall of the vesicle. 



The position and external appearance of the tubercle upon which 

 the duct opens has already been described (p. 160). In Figure 14 

 (Plate 1) is shown a section in the long axis of the appendage through 

 this tubercle. It is seen that the base is much constricted by an infold- 

 ing of the integument on the anterior side. This is the toothed process 

 referred to on page 161. As the duct passes through this narrow region, 

 it is constricted, but within the tubercle again enlarges. It opens 

 through the middle of the integumental membrane which covers the 

 face of the tubercle. This opening varies in different specimens from 25 

 to 40 micra in diameter (Figure 14, of. ex.). The tegumental membrane 

 is composed of three layers, which, passing from within outward, are, 

 (1) the thin non-calcified layer of the shell ; (2) the non-pigmented cal- 

 cified layer (Figure 14, la. ex.) ; (3) the cuticula or enamel layer. The 

 pigmented calcified layer (Figure 14, la. ex'.) stops abruptly at the edge 

 of the truncate face of the tubercle. The three layers of the membrane 

 are traceable into the duct on the anterior side, but not on the posterior. 

 However, even on the anterior side these rapidly thin out and disappear 

 entirely at a short distance from the outer face of the membrane. This 

 continuation of the integument into the anterior floor of the duct forms 



