320 THE DOLABELLINAE. 



lower layers of the cuticle, and gradually decreases, and becomes blended with 

 the strata toward the middle and upper portions. In the outer layers the cuticle 

 appears entirely homogeneous, save for the indications of the successive parallel 

 layers of deposition from the epithelial cells. 



At intervals among these smaller epitheUal cells single gigantic ones are 

 to be found, each of which lies at the base of a palatal spine, and apparently 

 produces it (Plate 9, fig. 8, b). These cells are usually found at the bottom 

 of slight depressions below the general level of the epitheUum. This matrix- 

 cell often reaches a diameter of 0.10 mm. in width by 0.04 mm. in height, extend- 

 ing the full width of the base of the overlying spine (Plate 9, fig. 3). The bulk 

 of the cell is finely granular, the upper portion, however, is often more coarsely 

 so, and is sometimes very vaguely limited, being broken up into a mass of 

 rounded granules of irregular size, underlying the base of the spine, the whole 

 appearance strikingly suggestive of poor fixation, which is very probably the 

 case. 



The very large somewhat flattened spheroidal nucleus occupies the basal 

 region of the cell, lying close to the basement-membrane. It contains clearly 

 defined chromatin granules, and one or two nucleoU. The basal portion of the 

 cell frequently bulges downward below the general level of the epithelium 

 and not infrequently extends below the bases of the adjoining cells as in Plate 9, 

 fig. 3. In some cases it somewhat resembles a large nerve-cell, but careful 

 study fails to reveal any trace of a nerve-fibre proceeding either from or to it. 

 In some sections, near the margin of the base of a spine, such cells appear to be 

 subepitheUal in position, as is seen in Plate 9, fig. 3, in the large cell adjoining 

 the matrix-cell of the spine. This is, however, the matrix-cell of an adjoining 

 spine not shown in the figure. 



All stages of the development of these palatal spines may be found scat- 

 tered irregularly in sections, as each spine passes through its developmental 

 liistory irrespective of its neighbors. One of the earliest stages is shown in 

 Plate 9, fig. 2. The finely granular matrix-cell is smaller than in later stages, 

 but is much larger than the adjacent ones. Upon its distal end, which arches 

 above the general level of the surrounding epitheUum, is borne a thin cap of a 

 highly refractive substance, the beginning of the young spine. In Plate 9, 

 fig. 4, the matrix-cell has much increased in size, and its chitinous cap has already 

 become so thickened that its substance appears in two layers. The apex of the 

 spine is already outlined by the obhque growth of the first strata. In Plate 9, 

 fig. 5, 6 further stages in development are shown, and they could be readily 



