120 BULLETIN OF THE 



The distribution of these mucous glands, like that of the kind first 

 described, is somewhat ii-regular, and the two kinds are about equally nu- 

 merous ; those of the larger kind are, however, much more conspicuous 

 by reason of their size. Both kinds of glands are found in the ejiidermis 

 as long as it persists over the surface of the scales. 



Chromatophores are abundant in the epidermis. They vary greatly in 

 size and shape, and are found in all parts of the layer. 



The boundary between epidermis and dermis is marked by the 

 presence of a distinct basement membrane. 



The dermis (Fig. 1), before it has begun to undergo modifications pre- 

 paratory to the formation of the scales, is only about half as thick (75 fi) 

 as the epidermis, and is composed of bundles of connective-tissue fibres 

 which may be divided into three sets according to the directions in 

 which they run. Two sets are parallel to the surface and diagonal to 

 the axis of the body, the third is perpendicular to the directions of the 

 other two. Of the first two sets, the fibres of one have a direction 

 backward and ventrad parallel to the direction which the rows of 

 scales will have later. The fibres of the other diagonal set cross 

 these in such a way as to make the dorsal and ventral included angles 

 a few degrees less than right angles, the anterior and posterior included 

 angles being consequently a little greater than right angles. The 

 fibres of the third set are much less numerous than those of either 

 of the other two, and, as they extend perpendicularly through the der- 

 mis, serve to bind together the different layers. Nuclei are irregu- 

 larly distributed among the filjres, as in ordinary connective tissue. 

 Blood-vessels are numerous, and ramify chiefly in the outer part of the 

 layer just beneath the basement membrane. Chromatophores are 

 present, as in the epidermis, and are found mostly upon the two 

 surfaces of the layer, being especially numerous at the deeper one 

 (Fig. 1). Upon the outer surface they lie at nearly uniform distances 

 apart (Fig. 4). Beside these color cells there is associated with them 

 at the deeper surface of the dermis, between it and the musculature, 

 quite a thick but very irregular sheet of finely granular white pigment. 

 Concerning the origin of this pigment I have been able to learn 

 nothing. 



The first indication of the formation of scales is a change in the outer 

 part of the dermis. There appear local thickenings of spongy tissue, 

 which are made up of many nucleated cells and a small number of fibres 

 lying among them without definite arrangement. These regions of 

 modified dermis are abundantly supplied with blood-vessels. At first 



