8 THE PERIODIC GKOWTII OF SCALES IN GADID.E 



inents, ils forment, non-seulement plusieurs ligncs cellulaires, mais les 

 canaux longituJinaux eux-memes se trouvent allonges. II est trus probable 

 que ces lignes collulaires ne se forment pas, seulement, I'une aprcs I'autre, 

 mais que plusieurs lignes sont produites simultanunient ; nous en trouvons una 

 preuve clans les ccailles, qui dans leurs accroissement successifs, conservent les 

 espaces marginaux, et dont les lignes cellulaires ou les cellules sont ainsi 

 separees en plusieurs groupes, nous citerons par exemple les c'cailles de cobitis 

 fossilis. Mais cet accroissement dans la pe'ripherie n'expliquerait nullement, 

 la grande t'paisseur du milieu ; nous en trouverons la cause dans la formation 

 de la couclie infurieure. Nous avons vu que celle-ci est composee de 

 plusieurs lanielles. A chaque accroissement se forment toujours des nouvelles 

 lamelles : les canaux longitudinaux, qui parcourent toute rccaille, apportent 

 les sues necessaires pour qu'une formation uniforme d'une nouvelle lamelle 

 puisse s'opcrer dans toute I'etendre de Tccaille. II s'ensuit, que les anciennes 

 lamelles rtant plus petites, IV'paisseur doit s'augmenter, a mesure que I'ou se 

 rapproche du foyer." 



As to the use of scales for purposes of classification, Mandl says that up to 

 the present " we have found definite and characteristic forms for each family," 

 and that further research on a sufficient number of individuals would decide 

 whether this might also be applied to genera and species. Mandl's views 

 were thus totally at variance with those of Agassiz, and the latter answered 

 in a letter addressed to 1' Academic des sciences,* in which he attacks the 

 results announced by his opponent. Agassiz concludes this letter by saying 

 that the description which he had previously given of the structure of scales 

 was correct, and that Mandl's method of viewing the subject was altogether 

 wrong. 



Mandl replied to Agassiz's letter by a counter letter, also addressed to 

 PAcademie.-]- He reiterated that scales are organised bodies, and consist of true 

 living tissue capable of nourishing itself and growing by intussusception. He 

 replied to each of Agassiz's criticisms by a new affirmation to the opposite 

 effect, and accused Agassiz of having badly understood or misinterpreted 

 some of his points. 



In the same year Agassiz published a fairly extended memoir, | in 

 which he takes up the facts as stated by Mandl, one by one, and subjects 

 them to the severest criticism. 



After some points relating to the structure of the skin, Agassiz deals with 

 the following : — 



(a) Longitudinal canals, (b) cellular lines, (c) the corpuscles, (d) the fibrous 

 layer, (e) the focus, (/) the teeth. 



Firstly, Agassiz denied the existence of true longitudinal canals, and the 

 role of these so-called canals as having the function of nourishing the scale. 



As to the cellular lines, Agassiz emphatically denied the presence of cells, 

 and wrote that Mandl had been deceived by an optical illusion. As to the 

 corpuscles, Agassiz maintained that they are not situated in the thickness of 

 the scale, as stated by ]\Iandl ; but on the contrary, close to the superior and 

 inferior surfaces, for if one slightly scrapes one of these surfaces or, after a slight 



• Agassiz, 1840. i Mandl, 1840. t Agassiz, 1840. 



