122 BULLETIN OF THE 



becomes modified over the scale papill?e to form an enamel membrane, 

 though this never becomes functional and the cells soon lose their 

 specialized character. Klaatsch studied the same form, and very 

 positively denies that any such modification takes place. He says 

 (p. 159): " Speciell die basale Epithelschicht liisst auch nicht die 

 geringste Yeriinderung wahrnehmen." In view of this conflict of 

 testimony, it seems more probable that the differences in the condition 

 of the basal cells of the epidermis observed by Hofer were due to vari- 

 ations in different individuals than to changes normally taking place 

 in the same individual. 



At a little later period these areas of dermal thickening have 

 extended laterally until their edges have become confluent, and the 

 dermis may then be described as made up of two layers, an outer 

 spongy layer and an inner fibrous layer, though no definite line of 

 demarcation separates the two. This is the earliest stage described by 

 Klaatsch. At the time when the formation of the scale begins, the 

 spongy layer in its thickest parts is about equal in thickness to the 

 deeper fibrous layer. The places in which scale formation is to take 

 place are indicated by a somewhat greater thickness of the spongy 

 layer. 



The scale first appears (Fig. 3) as a thin sheet of calcareous secreted 

 matter in the midst of the outer layer of the dermis. It is' surrounded 

 on all sides by the dermal cells, which lie thickly accumulated around it 

 and cover it on its outer surface from two to four cells deep, completely 

 separating it from the epidermis. Around its margin the cells lie closely 

 packed, and at the posterior edge are particularly numerous. To these 

 dermal secreting cells Klaatsch has given the name " Scleroblasten," a 

 term which I shall adopt in referring to them. 



The scale plate is not quite parallel with the surface of the body ; its 

 posterior margin is very slightly inclined outward, and with the sclero- 

 blasts ai'ound it forms a low elevation against the base of the epidermis 

 (Fig. 3). 



Secreted matter is not deposited where blood-vessels from below pierce 

 the outer or scleroblastic dermal layer, and consequently openings through 

 the scale result at such places. These persist to form the canals which 

 pierce the middle area of the adult scale (Haversian canals of authors). 

 The vessels which traverse them ramify upon the outer surface of the 

 scale to supply nourishment to the overlying scleroblasts. No difference 

 in character could be detected between the cells on the upper and those 

 on the under side of the scale. 



