837 



3. " On the Microscopic Structure of the Scales and Dermal 

 Teeth of some Ganoid and Piacoid Fish." By W. C. Williamson, 

 Esq. Communicated by Edwin Lankester, M.D., F.R.S. 



The author commences his paper by stating that the structure 

 and modes of growth of fish-scales have been studied by many ob- 

 servers, especially by Leeuwenhoek, Agassiz, Mandl and Owen. 

 The first of these considered each scale to consist of numerous 

 superimposed laminae added successively to the inferior surface. 

 This view has been revived, with some important modifications, by 

 M. Agassiz, and especially applied to the scales of ganoid fish; 

 which he showed to consist of laminae of true bone, usually 

 covered with enamel (email), the latter often resembling the den- 

 tine of fishes' teeth. M. Mandl denied that ganoid scales had 

 been formed by such successive additions of laminae ; and Professor 

 Owen also opposed the idea, that they had merely been the result of 

 successively excreted deposition. The author then proceeds to the 

 examination of the scales of the following genera and species - 

 Lepidosteus osseus, Lepidotus semiserratus, L. Mantelli, and L.fim^ 

 hriatus^ Seminotus rhombifer, Pholidotns Leachii, Ptycholepis Bol- 

 lensis, Beryx, Dapidius orbis, and B. granulosus ; all of which ap- 

 pear to be constructed according to a common type — one singular 

 modification of which is seen in PalcBoniscus comptus and P. Beau- 

 monti, and another in Gyrodus and Aspidorhynchus acutirostris. 

 Still more elaborate complications occur in the scales of the Stur- 

 geon and of Platysomus parvulus, the minute structure of which, 

 is described. Then follow detailed accounts of another interesting 

 group of structures found in the genera Megalichthys, Holoptychius 

 and Biplopterus, in which the osseous tissues and their superficial 

 coverings are exceedingly beautiful and complicated. The next fish 

 examined is Macropoma Mantelli from the chalk. In this the true 

 bony operculum is studded over with dermal teeth, as is also the 

 posterior part of each scale; the portion of the latter, however, 

 which is subjacent to these dermal teeth, is not osseous, but consists 

 of thin laminae, which do not contain lacunae. The hollow viscus 

 found in the interior of the Macropoma, is shown to be a cylinder 

 of true osseous tissue, of a singular laminated structure full of lacunae. 

 The author rejects the idea of its having been a stomach, but thinks 

 that it may have served the purpose of an air-bladder. 



The structure and arrangement of the dermal teeth from the skin 

 of the Dog-fish are then investigated, and appear to resemble those 

 on the opercular bones and scales of Macropoma. Similar teeth are 

 described in the fossil skin of Hybodus reticulatus, from the lias of 

 Lyme Regis. In the latter, numerous small granules of calcareous 

 matter, having a concentric laminated structure, have been im- 

 bedded in the substance of the soft cutis, under the dermal teeth. 

 The corresponding dermal teeth from the Raia clavata are described, 

 and also those covering the snout of the common Saw-fish ; as well 

 as the very singular premaxillary bones of the Ccelorhynchus. 



From an examination of the dermal appendages of the fishes thus 

 cursorily enumerated, the author concludes — 



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