Setisory Structures of Young Dog- Fishes. 259 



fully teased with needles or bristles, and mounted as they lay. 

 Other methods gave substantially identical results, but the above 

 was found the most convenient. 



These clusters consist essentially of two kinds of cells, with 

 various intermediate varieties, all intermingled to form a compact 

 mass, shaped something like a cask with one end smaller than the 

 other, resting on the corium by the larger end, the smaller filling a 

 circular opening in the epidermis. 



The most conspicuous of the component cells (all of which are 

 perpendicular to the surface) are cylindrical, slender, about 

 .04"^- to .05"""- in length and from .003"""- to .006"""- in breadth, 

 each with a large, oval nucleus about .008"^™' long, and commonly 

 from one to three nucleoli (Figs. 2, 10 and 11). The cell-contents 

 are pale, slightly granular, and usually stain more deeply in the 

 proximal part of the cell, so that the distal half of a cluster is 

 much the paler after staining with carmine or logwood. 



The deeper end of these cylindrical cells is frequently slightly 

 flattened and expanded, where it rests on the corium, while the 

 exact limit of the other end is often difficult to make out. IVIany 

 of these columnar cells are more or less constricted at some point, 

 as if by pressure, and some part of the length of the cell may be 

 reduced to a mere filament (Figs. 12 to 17). The part containing 

 the nucleus seems to resist compression, and the cell may thus be 

 reduced to a fusiform body with a filament at either end, as in 

 Fig. 17. We are thus led directly to rod-cells, not unlike those 

 of other sensory structures (Figs. 14 and 19). In a single speci- 

 men, first seen floating free, the filament was distinctly varicose — 

 possibly an indication of its relation to a nerve fibril (Fig. 19). 



No serious attempt was made to determine the nervous supply of 

 these bodies. It was noticed, however, that the deeper end of a 

 detached cluster often presented an appearance of a tangled pu- 

 bescence, as if from the projecting ends of the filaments of the fusi- 

 form cells. Something of the mode of arrangement of these ele- 

 ments is shown by Fig. 14. It evidently presents no definite plan, 

 except that the outer portion of each mass is composed exclusively 

 of the columnar cells. 



Sheathing the outer end of each cluster, were flattened scales, 

 evidently modified forms of the superficial cells of the epidermis. 

 The appearance of those nearest the clusters is shown by Figs. 3 

 and 9, while Fig. 7 represents the form of those of the outer layer 

 of this sheath. 



