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XXIX. Investigations into the Structure and Development of the Scales and Bones 
of Fishes. By W. C. Williamson, Esq., Professor of Natural History, Anatomy 
and Physiology , in Owens College, Manchester. 
Communicated by Edwin Lankester, M.D., F.R.S. 
Received June 20, — Read June 20, 1850. 
In 1849, I had the honour of laying before the Royal Society a memoir on Lepido- 
genesis, in which I chiefly directed attention to the structure and growth of the 
dermal teeth and scales of Ganoid and Placoid fish*. Since the completion of that 
memoir, a large proportion of such leisure hours as could be snatched from the active 
duties of professional life, have been devoted to a still wider range of inquiry con- 
nected with the same subject. During the interval, I have made a great number of 
sections and other microscopic preparations of scales belonging to M. Agassiz’s 
Cycloid and Ctenoid orders, as well as of the Ostraciont family of his Ganoid order : 
the results of the investigation having convinced me, that the structure of these 
organisms has hitherto been very imperfectly known, I am not surprised that their 
genesis and development have been involved in considerable obscurity. 
A list of the various writers who have preceded me in this inquiry, was given in 
my last memoir. From this, it will be necessary to select two of the most modern 
observers, and to notice what their respective views are, in order that we may com- 
prehend the bearing of my more recent observations upon those of my predecessors 
in the study ; these are, M. Mandl and M. Agassiz. 
M. Mandl has published an elaborate memoir on Cycloid and Ctenoid scales, in 
vol. ii. of the ‘ Annales des Sciences Naturelles,’ in which he has developed his pe- 
culiar views respecting them. He has arrived at the conclusion, that Cycloid scales 
consist of two portions. “ Nous avons ainsi acquis la preuve que la plupart des 
ecailles sont composees de deux couches superposees ; I’inferieure olfre la structure 
des cartilages fibrineux, la superieure, celle des cartilages a corpuscules ; cette derniere 
est pourvue en outre de lignes, dont nous demontrons Torigine, par la fusion de 
cellules primitives ; ces deux couches sont parcourues par des lignes longitudinales, 
qui appartiennent aux deux couches'f'.” Observing certain radiating lines proceeding 
from the centre towards the circumference, especially in the anterior portion of the 
scale, he concluded that they were nutrient canals, which conducted the fluids from 
the skin to the centre of the scale, which he designates le foyer,” and which he 
* Philosophical Transactions, 1849, Part II. p. 435. 
t Annales des Sciences Naturelles, vol. ii. p. 348. 
