156 University of California Publications in Zoology ['Vol. 13 



V. The Complexity of the Dorsal Scale 



In a half-grown specimen there are scales at the beginning of the 

 caudal fin, which, although above the lateral line, are unlike those 

 of the dorsal type (see fig. E). These may be described as more or 

 less triangular in form, the tip of the scale representing the apex of 

 the triangle. From the base of the triangle there is an anterior pro- 

 jection similar to the anterior arm of the ventral type of scale. 



In the same area from which these scales came there are present 

 other and larger scales which are entirely of the Greek-cross pattern. 

 Between these two extremes there are numerous scales intermediate 

 in complexity. Since these types occur together the question arises, 



/o. ^post.a. 



Figs. E-G. — Dorsal scales showing increase in complexity of the dorsal type 

 of scale from the immature scale E through stages F and G. X 27. Dorsal 

 view. For explanation of parts see figures C-D. 



do the triangular scales represent a definite type, or are they imma- 

 ture scales which by growth will reach the complex Greek-cross form ? 

 In order to study this point, a series of scales from the triangular to 

 the Greek-cross tj^pe has been dissected out. The first of these (fig. E) 

 we have just described as triangular in form, and the last one of the 

 series (fig. J) is essentially like the type of dorsal scale previously 

 described. 



In the second scale (fig. F) the triangular appearance is reduced. 

 This is due to the fact that in such a scale the lateral arms are elong- 

 ated, and the sides ©f the triangle from the lateral arm to the tip of 

 the spine have become concave ; the latter condition is due to the fact 

 that near the tip of the lateral arms considerable growth has taken 

 place backward and outward. 



In the third (fig. G), significant growth changes are evident. The 

 anterior and lateral arms are strong, and the posterior arm is devel- 

 oping. The anterior arm is notched in front and is surmoiuited by 



