SCALE OBSERVATIONS OF THE SQUETEAGUE AND PIGFISH. 297 



Mandl (1839), on the other hand, considered scales living tissue capable of growth 

 by intussusception and consisting of two layers, the superior and the inferior. The 

 inferior layer is laminate, while the superior layer is cartilaginous, the lower part being 

 interspersed with calcareous corpuscles. The growth of the superior layer is peripheral, 

 while that of the inferior layer takes place by the addition of secretions from the floor 

 of the scale pocket. He described the corpuscles as separate elements or cells in the 

 superior layer, in definite positions, and of a yellow color which disappears on acidulation. 



Peters (1841) agreed with Mandl as to the laminate structure but with Agassiz 

 as to the location of the corpuscles, with the exception that he was unable to find them 

 on the surface of the superior layer. 



Williamson (1849) followed, adopting the opinions of Agassiz, Mandl, and Peters, 

 with modifications. He stated that there were three layers, the superior, the inferior, 

 and the median. The superior layer differs both in structure and origin from the other 

 two layers. In section it presents the appearance of an undulating outline with a very 

 faintly laminate interior structure. It extends entirely to the periphery. In early 

 stages it is a soft membrane which later calcifies. In substance it resembles the ganoin 

 of Lepidosieus {Le pis os feus). 



The median layer is built up of a mass of lenticular calcareous bodies which unite 

 with one another as they increase in size, losing their shape in this coalescence. In 

 thickness it decreases from the center to the periphery until it disappears, leaving the 

 periphery flexible. After the fusion of the corpuscles the median layer splits up into 

 horizontal laminae which agree in direction with the membranous laminae which exist 

 previous to calcification. 



The inferior layer consists of numerous membranous laminae arranged in parallel 

 horizontal lines more numerous at the center, only one appearing at the periphery. 

 Each lamina is composed of fibers, all parallel with each other. They are the result of 

 the calcification of the laminae and have their origin as small centers of calcification 

 which grow in size by the addition of layers to the outer surface, in section giving the 

 appearance of concentric rings. Growth takes place by the successive increase in size 

 of the laminae of the inferior layer. 



Salbey (1868) says that the inferior layer consists of thick lamellae, separated by 

 thinner ones. The thin lamellae are conjunctive, while the thicker ones are calcareous. 

 The thinner ones finally calcify and fuse with the thicker ones, giving the older scales 

 the appearance of having fewer laminae, while they really have more. According to 

 him, the mode of growth is that the inferior lamina is fastened by a conjunctive sub- 

 stance which eventually calcifies, after which calcification another layer of the con- 

 junctive substance is added, which in its turn calcifies, etc. 



The work of Baudelot (1873) is in greater detail than that of any of the foregoing 

 authors and probably of more value. He states that calcium phosphate and carbonate 

 constitute the inorganic substance of the scale. He described the tissue of scales as 

 being a striated substance separable into laminate folia. Corpuscles are more abundant 

 in the exterior laminae and comparatively rare in the inner ones. They increase in 

 size with age and two or more may fuse. They represent products of a crystalline nature 

 and exhibit a series of concentric lines from the center to the outer surface. 



The origin of a scale is a calcified spot which slowly extends until it becomes a lamina. 

 The scale always adheres by its inferior surface and periphery and always grows by the 



