42 Descriptions of Preparations. 



Parker (Shoulder Girdle, p. i6.), as being" merely a 'scale bone/ 

 Similar muco-nervous organs are to be seen upon several of the 

 dermal bones of the head^ especially upon the scaleless praeoper- 

 cular and dentary bones. 



As is the rule in Acanthopterygii with two dorsal fins^ all the 

 rays of the anterior one are rigid and spinous. The first of the 

 thirteen fin-rays of the second dorsal is similarly rigid, as are two 

 of the anal, and one of the ventral. All the pectoral fin-rays are 

 soft and jointed. 



For the general anatomy of fishes, with remarks as to its bearing 

 upon their zoological position, see Miiller, Vergleichende Ana- 

 tomic der Myxinoiden, 1838-1845; Rathke, Darmkanal und 

 Geschlechtstheils der Fisclie, 1824, especially p. 7 and p. 

 121 ; Cuvier et Valenciennes Hist. Nat. des Poissons, vol. i. 

 1828, p. 201 and p. 419. 



For a detailed account of the anatomy of the perch, see Cuvier and 

 Valenciennes, vol. ii. pp. 28-30, pi. i.-viii., with plates. 



For an account of the brain, see Gottsche, Miiller^s Archiv., 1835. 



For the Thymus, see Stannius, Handbuch der Zootomie, i. 256 ; 

 Leydig, Handbuch der Histologic, p. 43 1 . 



For the lateral line, see Macdonnell, Transact. Royal Irish Academy, 

 vol. xxiv. 1862, p. 169, and F. Leydig, Nova Acta, 1868. 



For the terms employed in zoological description, see British Mu- 

 seum Catalogue of Acanthopterygian Fishes, by Dr. Giinther, 

 1859, ^^^- ^' V' ^^- ^^^ P- 5^} ^^^ YarrelFs British Fishes, 

 vol. i. 



12. Skeleton of Common Perch {Perca Fluviatilis). 



The perch, and indeed the entire Acanthopterous order to which 

 it belongs, may be taken as illustrations of highly specialized, as 

 opposed to high types of organization ; as they accumulate in their 

 economy a large number of the peculiarities of their own class 

 rather than show any affinity, as do the ganoids, to forms of life 

 higher in the scale than themselves. 



One half of the moveable vertebrae are caudal, and by the 

 absence of ribs and transverse processes, and by the presence of 

 three vertical fins in this moiety of the animaFs body, great power 



