118 BULLETIX OF THE 



former is much the better ; the h%tter is especially useful in the 

 study of the glands of the epidermis and in bringing cell membranes 

 into prominence. 



The young Lepidosteus in which I found the earliest indication of 

 the formation of scales was about 145 mm. long and a little over 

 eighteen months old. Klaatsch has stated that the scales appear upon 

 the dorsal side of the body earlier than upon the ventral, and as the 

 material studied was taken in this specimen (as in most cases) from 

 near the ventral line, it is probable that the scales begin to form upon 

 the dorsal portion of the body at a somewhat earlier age. 



Before the l)egiuuing of the formation of the scales the integument is 

 about 225 fj. thick. The epidermis is nearly twice as thick as the 

 dermis and is made np of numerous layers of spheroidal or cuboidal 

 cells (Fig. 1). The cells of the deepest layer are somewhat elongated 

 in a direction perpendicular to the surface, and consequently have the 

 appearance of indistinctly columnar epithelium. 



There are two kinds of glandular structures present in the epidermis. 

 Those of one kind have a spherical, or more often ovoid or oblong form, 

 with the greater axis perpendicnlar to the surface of the body, and 

 appear in sections as spaces of corresponding shaj)e. The long diameter 

 in the larger of these spaces is not infrequently (Fig. 1) from one half 

 to two thirds the thickness of the epidermis (75-100 ^i). 



The glands are quite irregularly distributed, some areas being only 

 very meagrely provided with them, while in others they are so crowded 

 as to leave little more than thin filmy pai'titions between them. 

 Sections parallel to the surface in such areas present a net-like appear- 

 ance, tlie empty gland cells corresponding to the meshes. To each 

 space there belongs a flattened nucleus, which is closely applied to the 

 wall near its deep end. The whole structure is doubtless to be con- 

 sidered as a single cell which has taken on a secretive function, — a 

 unicellular gland. 



These glandular spaces sometimes appear empty, but are more often 

 found partly filled by an indistinctly granular colorless substance 

 (coagulum), pi'obably precipitated by reagents from the fluid or semi- 

 fluid secretion which they held during life (Plate I. Fig. 1, Plate II. 

 Fig. 16). I do not find that these spaces have any means of communi- 

 cation with one another, and only vei'y rarely do I find one having an 

 opening to the exterior. Klaatsch has described these as mucous 

 glands. I liave no doubt that they are concerned in the production of 



