284 Dr L. Mandl's Besearehes on the 



there is no break throughout its whole length. In the two teeth imme- 

 diately below these, the development is much less advanced, the ends 

 are truncated ; the external layer of the tooth does not entirely envelope 

 it, but the roots can be distinctly observed, and we can even notice the 

 roots of the different layers. Figure 15 likewise shews the different de- 

 grees of development, until we arrive at teeth of the most elementary 

 kind, covered with corpuscles, ill defined, rounded, and very little de- 

 veloped. 



We shall now describe a few forms in the different families of fishes. 



The Gobioides have a simple series of truncated teeth ; the truncated 

 surface is unequal, and of a deeper colour than the rest of the scale ; the 

 roots are sometimes very distinct, as well as the envelopes ; their mem- 

 brane is separated from the rest of the scale by a line. 



The PerciJides present well pointed teeth in the first series ; the others 

 are nearly square, and their sacs are visible at the sides ; their position is 

 alternate. 



The Solea nasuta is provided with pointed teeth in all the series. It is 

 very difficult to understand their position on these scales, on examining 

 tliem for the first time, because the roots and lower portion of the sac of 

 the upper tooth are covered by the end of the tooth and the sac of the 

 inferior one. It is necessary to pay great attention in making the first 

 observation. 



In Sargus annularis, the teeth of only two or three of the first series 

 are very distinct ; the others are rudimentary and inconspicuous. 



In the numerous scries of teeth to be found in Mugil cephalus we have 

 an opportunity of studying their successive development in detail. In 

 the series next the focus, round sacs exist having a rounded germ in the 

 interior ; beyond that the sac is elongated into a point, the base of the 

 teeth appears, the roots are developed, the pointed termination begins to 

 form, and the entire tooth is at last confounded with the sac. The form 

 of these teeth is ovoid, their position alternate. The teeth found nearest 

 the focus, or rather what may be called the germs of teeth, are not very 

 distinct, for they arc covered with corpuscles and broken cellular lines. 



Teeth are found on a portion of the scale which, among manyfislies^ 

 such as Tringla, is easily destroyed, by being steeped in spirits of wine ; 

 this part then falls off along with the teeth, and it is always found sepa- 

 rated at the place where the line occurs, which divides the teeth from 

 the rest of the scale. The same fact is observed among the Gobioides, &c. 



The teeth are always most numerous in the middle of the terminal field, 

 and they diminish in proportion as we approach the lateral edges, until 

 at last we arrive at an insulated tooth. 



Formation of the Scale. — If we would apply the results obtained by 

 studj-ing the intimate structure of scales, to the explanation of the man- 

 ner in which they are formed, we will at once perceive, that it is of im- 

 portance to distinguish between the formation of the superior layer and 

 that of the inferior. The former composed of cells, and their bases witU 

 the tissue containing the corpuscles, acquires its development by the 



