MUSEUM OF COMPARATIVE ZOOLOGY. 153 



according to the stain employed. The greatest number of structu- 

 ral details are obtained from those lightly stained with hscmatoxylin. 

 Sections thus stained are represented in Figures 6, 7, and 8. Though 

 evidently differentiated hypodermal cells, they lie almost entirely in the 

 cutis, enveloped by a delicate coat of connective tissue, in which can be 

 found occasional flattened nuclei. The distal half of each cell is occu- 

 pied ill great part by a large vacuole, directly continuous with that of 

 the adjoining cell. The space thus formed measures 12 X 15 X 25 fi, and 

 communicates with the exterior by means of a narrow canal opening 

 simply on the surface of the cuticula. The duct measures 6-8 fx in di- 

 ameter, and at the distal end of the cell does not lie in the centre of 

 the neck (Fig. 9). The connective-tissue envelope does not penetrate 

 between the cells, which in consequence are separated onli/ by their own 

 membranes (Fig. 6 or 1 1,*), and these, continued over or under the distal 

 vacuole, appear, if the cell be viewed along the plane of the partition, 

 to bisect the vacuole (Figs. 6, 10), the latter suffers, however, a slight 

 constriction along this line, so as to impart to it in transverse section a 

 biscuit-shaped appearance (Fig. 7). Its longitudinal section is cordi- 

 form, as shown in Figure 6. The two large clear spherical nuclei, 9 /x 

 in diameter (Figs. 10, 11), may be differentiated with carmine or saf- 

 franin, and then appear in the lower half of the cell, usually nearly 

 symmetrical to the dividing membrane. Each displays a single central 

 deeply stained nucleolus, and many minute chromatine gi-anules. If the 

 plane of the section pass transversely below the vacuole (Fig. 11), the 

 cells are seen to possess a hemispherical form, and the dividing mem- 

 brane to make an S-shaped curve. 



Whether active or resting, a clear zone of plasma forms the periphery 

 of the cell on all sides, and is therefore adjacent to the vacuole, as well as 

 to the external surface of the cell. This zone is traversed radially by 

 delicate fibrils, the beginnings of the plasma reticulum which fills the cell, 

 but which ordinarily is easily seen only in this clear zone. In eveiy sec- 

 tion one finds a few cells of this sort, which, besides an empty vacuole, 

 exhibit this reticulum very plainly throughout the entire faintly tinted 

 cell body (Fig. 8).^ They are evidently the functionally inactive or 

 resting cells. The first stage in secretion is seen in the accumulation 

 of numerous granules in the basal portion of the cell (Fig. 6), which 

 are stained deeply with hsematoxylin, and by continual aggregation 



1 Strictly speaking, Figure 8 represents the last phase in secretion. The first 

 differs only in the absence of matter in tlie vacuole, and of the few granules just 

 below it. 



