322 THE DOLABELLINAE. 



merge into the zone b, in wliich the homogeneous secretion increases in amount 

 and staining quality, appearing ahnost black with hematoxyUn at the point 

 of discharge, a. In other sections this secretion, evidently of a mucous nature, 

 is seen issuing between the epithehum-cells, and is especially abundant in the 

 deeply infolded groove shown in Plate 9, fig. 7, near the free margin of the flap. 

 Here the secretion accumulates in considerable amount, and issues between the 

 thick cuticle of the spine-bearing area and the epithelium just beyond it. 



Other very characteristic gland-cells are scattered just below the epithe- 

 hum of the dorsal surface of the fold. Many of these show no connection 

 with the surface, while others are united by more or less slender neck-like pro- 

 longations. A group of these cells is showTi, Plate 8, fig. 6. Deeply staining 

 nodal granulations of varying size and shape are abundant in them. Unfortu- 

 nately the fixation of the hmited amount of material at hand does not permit 

 any trustworthy conclusions to be drawn concerning them. 



The epitheUum of the palatal folds rests upon a narrow layer of dense con- 

 nective-tissue, below which are found bundles of smooth muscle-fibres, running at 

 various angles, and surrounded by a large amount of fibrous connective-tissue. 

 The central area of the fold is occupied by looser connective-tissue, in which scat- 

 tered bundles of longitudinal muscle-fibres are located. At the base of the sec- 

 tion, Plate 9, fig. 7, is shown the duct of the salivary gland in cross-section at d. 



In Dolabella hasseltii (Fer.) similar relations of the palatal spines to the 

 epitheUum and the cuticle were made out, with some differences worthy of note. 

 In this form the spines are slender, thick-walled, tapering tubes, the thickness 

 of the walls increasing and decreasing at regular intervals in coincidence with 

 a system of parallel ridges and depressions of the outer surface. Each spine 

 is the product of a single matrix-cell, the central free end of which is prolonged 

 into the tubular base of the spine, while the wall itself is secreted by the zone 

 of the cell-surface around this projection. Thus the spine fits down over the 

 prolonged tip of the cell in the form of a conical cap, the successive layers of 

 chitinous substance being in the main secreted by the sides of the distal end. 

 The central portion, however, takes part in this secretion at intervals, the 

 layers then formed appearing as several curved dome-like sheets, bridging across 

 the entire lumen of the spine and continuing downward as part of its sides. 

 No indication of the participation of any of the surrounding cells in this secre- 

 tion could be foimd, nor is anything here present similar to the small central 

 cell which determines the cavity in the spicule-development in the Solenogastres, 

 as described by Heath (1911, p. 28). 



