294 BULLETIN OF THE BUREAU OF FISHERIES. 



SPINES. 



Kuntzmann (1824) described what he regarded as two distinct kinds of spines: 

 (i) Spines which molt, and (2) permanent spines, which are integral parts of the supe- 

 rior layer of the scale. Mandl (1840) thought spines were comparable to true teeth. 

 Leydig (1851) regarded them as extensions of osseous corpuscles, a view shared also 

 by Peters. Salbey (1868) considered them as integral parts of the superior layer appear- 

 ing successively at the posterior margin of the scale and which constantly wear away. 



Baudelot (1873) gives a detailed description of dll the variations of spines, which is 

 too long to reproduce. He concludes, among other things, that their number increases 

 with age and on different parts of the body, and in places where they are rudimentary 

 they may drop off, leaving cycloid scales. He advances the theory that the spines 

 have their origin in the serrae on the edges of the posterior circuU. In support of this 

 hypothesis he uses the following arguments : 



In many scales * * * the edges of the circuli present a series of very distinct microscopic 

 indentations, and in some ctenoid scales the spines are so small as txj appear only as indentations of the 

 circuli of the posterior region which have become very prominent. In many cycloid scales the posterior 

 region shows a series of tubercles arranged witli as much regularity as the spines and presenting a striking 

 analogy to these structures. These tubercles are, however, only partial thickenings of the concentric 

 ridges (circuli). In tlie same fish the scales become altered and pass from the ctenoid to the cycloid 

 condition, and in that case it frequently happens that the spines become replaced by simple ridges." 



This substitution is to him sufficient proof of the homology of the spines and the 

 circuli. 



Klaatsch (1890) makes the cycloid scale typical of teleosts, because "(i) it repre- 

 sents simple conditions, and (2) it supplies a suitable object for placing the skin covering 

 of the teleosts in line with the selachians and ganoids." He regards the ctenoid scale 

 as the result of still further specialization in the teleosts. 



Ussow (1897) thinks that there is no relation whatever between placoid teeth and 

 the spines of ctenoid scales, but that the similarity is purely accidental. He thinks 

 that spines are formed of the same substance as the superior layer of the scale — the 

 hyalodentine of Hofer. 



Tims (1906) finds in the minute projections on the scalelets of the cod the ante- 

 cedent form from which the spines of ctenoid scales are derived. If these projections 

 (which he finds more prominent on the posterior field) be more pronounced and slightly 

 more perpendicular, we have the spines of ctenoid scales. 



Cockerell and Moore (1910) advanced a somewhat different theory, as follows: 



The teeth arise through the modification of tlie apical ends of the vertical circuli, i. e., circuli which 

 in the apical region retain their vertical position. It is not evident that they have anything to do 

 with the radii. In very highly specialized ctenoid scales * * * the teeth form a separate fringe 

 which appears to have no intimate connection ^vith tlie rest of the scale. It follows that a scale with 

 completely transverse apical circuli can not be, and can not become, ctenoid. The reason why there 

 are no ctenoid cyprinid scales seems to be that the group has advanced too far along the line of modi- 

 fication in regard to the circuli to be able to produce them. 



" Translation by Thomson. 



