292 BULI.ETIN OF THE BUREAU OF FISHERIES. 



CIRCULI. 



The concentricity of the circuli suggested their connection with growth as early as 

 1716, when Reaumur said of them: "They occupy the borders of each layer and they 

 represent different degrees in the growth of scales." 



It seems that the difficulty in cutting cross sections has been largely responsible 

 for the confusion as to the nature of the circuli. They have been variously regarded as 

 the ends of laminae, grooves for blood vessels, "cellular lines," growth rings, crossings 

 of transverse fibers in the superior layer, etc. 



Peters (1841) admits a difficulty with the circuli. He contends that they are not 

 the ends of laminae, because they are not always parallel with the outer edge of the 

 scale, but are sometimes perpendicular, a condition that could never occur in the case 

 of lamina edges. His only attempt at explanation was that "the crossing of the fibers 

 in the superior layer seems to explain the circuli." 



Agassiz (1834) thought that the number of circuli agreed with the number of 

 laminae in the inferior layer, but Peters was never able to bring himself to this opinion. 

 Blanchard (1866) rejected this theory because he found that in some species the 

 number of circuli is the same in the young as in the old. 



The "cellular lines" of Mandl (1840) are explained thus: "The laminae are not 

 superimposed layers, but have their origin in special cells in the superior layer and 

 finally become lines" — a rather vague explanation. 



Salbey (1S68) attempted to show by vertical sections that they have no connection 

 with the laminae, but that they belong to the superior layer, and may disappear or 

 be replaced, or new ones may be interposed between them. 



Baudelot (1873) gives a thorough description of the circuli imder the following 

 scheme : 



1. Presence: (a) May be present over the entire scale ; (6) may be partially present (on the periph- 

 ery); (c) may be absent. 



2. Disposition: (a) Concentric; (^) regularly concentric at periphery, irregular at center. 



3. On posterior field: (a) Sometimes appear; (6) sometimes very rare, losing their regularity and 

 becoming enlarged at certain points or covered with tubercles. 



4. Other modes of orientation; (a) Perpendicular with contour, but parallel witli each other. 



5. Number: (a) Greater in anterior tlian in lateral field; (6) greater in lateral than in posterior field. 



He fuids the form of the circuli to be a ridge with its edge turned toward the focus. 

 Its edge is somewhat serrate, resembling the teeth of a saw. He notes zones where 

 circuli appear to be closer together. He considers the circuli as having some relation 

 to the moorings to the body, suggesting them as holdfasts. To show that they are not 

 edges of laminae he makes the following observations: 



(i) The circuli very rarely effect a complete arrangement in the form of concentric lines; (2) the 

 circuli may be perpendicular to the contour of the scale; (3) they may show the most irregular arrange- 

 ment, become folded up against one another, entangled in all directions, or even form a sort of network 

 of irregular meshes ; (4) the circuli are appendages of the superficial layer of the scale ; (5) they originate 

 at the margin of the scale as points of isolated calcification ; (6) they show a marked inclination to the 

 focus. 



To sum up his conclusions, he rejects Agassiz's idea that the circuli are the edges of 

 laminae. He considers them as related to the mooring of the scale to the integument, 



